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Secrets Hidden in Images (Steganography) - Computerphile

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Secret texts buried in a picture of your dog? Image Analyst Dr. Mike Pound explains the art of steganography in digital images. The Problem with JPEG: https://youtu.be/yBX8GFqt6GA The Bayer Filter: https://youtu.be/LWxu4rkZBLw Super Computer & the Milky Way: https://youtu.be/5KEhhW8TOGk JPEG Discrete Cosine Transform (DCT): https://youtu.be/Q2aEzeMDHMA http://www.facebook.com/computerphile https://twitter.com/computer_phile This video was filmed and edited by Sean Riley. Computer Science at the University of Nottingham: http://bit.ly/nottscomputer Computerphile is a sister project to Brady Haran's Numberphile. More at http://www.bradyharan.com
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Text Comments (412)
Lance Sellner (4 days ago)
Hello, anyone here? Im wondering how long it would take to hand-encrypt an image using DCT.
P Last Name (6 days ago)
Nobody has commented on this for at least two years. I guess it's old hat.
Topher TheTenth (12 days ago)
I'm not understanding this at all. My understanding of a bitmap is there are three values per pixel: Red, Green, and Blue. Each of them ranges from 0 to 255. Make a list of 1st-pixel Red, 1st-pixel Green, 1st-pixel Blue, 2nd-pixel Red, 2nd-pixel Green, 2nd-pixel Blue. In this list of integers (each ranging from 0 to 255) , the occurrence of odd numbers and even numbers will be ABSOLUTELY RANDOM, won't it? And whenever any absolutely random key is added to a message that isn't random, the result is absolutely random. The process of steganography would then consist of translating your message into a series of 0s and 1s and writing those digits down a column to the right of your list of color-integers. Then you use a convention such as "0 means even, 1 means odd". Where you have a zero in the column that is the message to be encoded, if the color-value integer to the left is even, write it in yet another column to the right, unchanged. But if that color-value number to the left is odd, write, in the rightmost column, the number that is ONE FEWER than that number. So, 255 changes to 254, and 1 changes to 0. All odd numbers in the range from 0 to 255 can be so transformed without exceeding the range 0 to 255. Where you have a "1" in the message to be encoded, and it lies to the right of an odd number, write that odd number in the rightmost column unchanged. But where a "1" lies to the right of an EVEN number, change that even number to odd by ADDING (not, as previously, subtracting) 1 to it. So, 254 changes to 255, and 0 changes to 1. All even numbers in the range 0 to 255 can so be handled without exceeding the range 0 to 255. You can't just do a -1 or +1 modulo 256 for this, because that would involve changing some occurrences of 255 to 0, and some occurrences of 0 to 255. Changing a color-value of a pixel by a value of 255 could create a noticeable scar vs. when the greatest change is only "1". Then just group all of the color-value integers back into triplets for each pixel, and assemble all the pixels back into a photograph. It will be indistinguishable (to the human eye) from the original, AND the oddness/evenness of the values for each component of each pixel's colors will be as random in the output as it was in the original. (So no computer is going to notice that its randomness is different from the randomness of untweaked photos.) The person receiving the photo divides it into pixels, and divides each pixel into three integers (Red, Green, and Blue) each ranging from 0 to 255, and considers only their evenness and oddness, and writes a "1" for every odd value and a "0" for every even value. Thus the recipient obtains the binary message that was sent.
Domício (17 days ago)
Great content.
Andrew Potapenkoff (18 days ago)
This stuff reminds me of QR code.
miss misanthropist (18 days ago)
so this is how spore stored stuff inside pngs
Bear Grylles (19 days ago)
6:00 started becoming a foreign language somewhere around here.
CTA 91 (19 days ago)
theee bits! theee bits!
서찬욱 (22 days ago)
secret message in my profile picture
Fester Blats (22 days ago)
So using this method for copyrighting images means that they actually ruin them. That doesn't sound very clever.
Mythricia (11 days ago)
Ruin? The change is literally invisible unless you have the source image.
Bikal (27 days ago)
They're trying to build an intersect.
fpolloa (30 days ago)
Can you do the same with music?
iExotic (24 days ago)
At 7:28 the inerquartile computing unit is actually incorrect. I've studied it for about 3 years now and the complexion of the quadratic formula is hidden in the JPEG code. Cause if you document.write (a_bc) + SQL a=0b it will result in the quaritization of 0, hence the quadratic code is equal to 0, so it can't be it. Check my reply for my proof.
zionlee1004 (1 month ago)
LohnS (1 month ago)
Amazing stuff
Raymond (2 months ago)
haha, love the video :D
_____ (2 months ago)
Expand upon this by doing a video on Numbers Stations!
Muradean (2 months ago)
I did a small amusement app, "The Steganographer", with Javascript and PHP this Summer. The Big image should be atleast 4 times bigger than the one to be hidden. Don't forget besides the RGB components you can also use the ALPHA channel(the channel for transparency) to hide some bits!That increases the amount of info you can hide per pixel. Curiosity: The alpha channel on PHP has only 7 bits while alpha in Java(not Javascript) has 8 bits. You should also know that since .jpeg is not a lossless format, each time you create a .jpeg(to hide the small image in the big one), the data will be compressed( the string of bits will be slightly changed), so after when you try to extract the original data from the .jpeg(the smaller image) you won't be able to do that perfectly. A solution is to use .png, which is heavier but gets the job done cause it is not a lossless format. You can check The Steganographer of my channel if you want to.
Couldn't pirates clear any contained water marks in the image/video by running it through a program that simply scrambles the last two values of every pixel? This would create an imperceptible difference in the image/video but clear any messages/marks within. I could imagine pirates and/or websites deploying this automatically on uploads, just in case. I mean, messages could be hidden in other bits but as stated in the video these values are much more noticeable.
CROOK53Y (3 months ago)
goochlands finest (4 months ago)
could you use this on a 10 hour nyancat video frame by frame??
Secrets to Success (4 months ago)
This gentleman, Dr Mike, is absolutely fascinating... I only discovered this channel yesterday and Ive viewed a lot of the videos already.
kebman (4 months ago)
Now imagine steganography on DLL files, programs and databases!
kebman (4 months ago)
Now imagine steganography on film and sound...
kebman (4 months ago)
Would steganography even work on Facebook or Instagram? Don't they re-arrange and re-compress the file? Wouldn't that effectively erase the message?
Mythricia (11 days ago)
If they re-encode the images, the message is probably lost using any of methods described in the video. But, there are other methods, such as breaking the image up into "blocks" of some size (just as a random example, say 4*4 pixels). Then you encode the 1's and 0's using those blocks. This is slightly more resilient to changes, because even if some pixels change, you can use the average value to determine what the original data probably was. You can also include error correcting codes, and so on.... Now, this all rather quickly decreases the amount of data you can store. You are trading away a lot of your available "space" for redundancy and resilience. But if all you need is to watermark the image, with a just a simple string of text only a few dozen bytes long, you would able to add a really huge amount of redundancy and resilience without worrying, and just repeating the message over and over across the image, including all the safeguards. That becomes a lot more difficult to remove.
kebman (4 months ago)
I don't know about you, but I'd start looking for steganography on 4Chan lol!
Antediluvian Spy (4 months ago)
I would pay Forbes list figure sums to have Dr. Mike Pound be the teacher of every bit of knowledge I learn for the rest of my life. Time to rob Warren Buffet.
rick dalton (4 months ago)
I must have watched a million Tech videos and read three times as many online articles before I found this guy here on computerphile and I have come to realize without question that this man is dangerous. Very few people possess this level of knowledge and the videos are by far the best on the internet. Keep up the good work!👍👍
This message contains top secret nuclear project information... just kidding. . . *OR AM I?*
Jonathan Cook (7 months ago)
sinta dorti (7 months ago)
Zewos and wons !
Bambel (7 months ago)
I am very glad you didn’t just show us the image and have us take your word for it that the images were different!
I highly doubt that image steganography approach that accounts statistics can be cracked without the source image, anyone can proove me wrong?
Last (8 months ago)
I think I should Start studying in Nottingham...
444 444
Danny Foldager Thomsen (9 months ago)
I was struggling with a stego CTF when this video just popped up. Thanks, it helped me solve the challenge :)
Mister Hat (9 months ago)
A pixel is 4 bytes? Normally it's three unless there's an alpha channel or the data is padded to four bytes. In either case, changing that fourth byte is going to be obvious (because it's likely to be zero.)
ArchaicVirus (9 months ago)
Zed is probably used instead of 'z' to avoid confusion, as z sounds like c, or b for example. Its like how americans use charlie, or bravo, to indicate c, or b, for the same reason.
Matt T (9 months ago)
Interesting... Could someone exploit this in order to hide scripts inside of images? If that is the case, how could one protect themselves from this exploit?
muhammad nauman (10 months ago)
what paper is he using to write on?
Burak Kaymakci (10 months ago)
I really love your videos but one thing I would really appreciate is that subtitles, especially in Dr. Mike's videos, please. I am really having a though time to understand his accent sometimes. 😅 And the present subtitles are not correct. Thank you for the great videos! :)
Facehunter2003 (11 months ago)
Meta data changing, one way to hide stuff :P
Richard Smith (11 months ago)
Technically, you could modify the least significant bit of all three color channels to give you three bits per pixel. For a 1920x1080 picture, that would give you enough space to embed a message that is (1920*1080*3) / 8 bytes large, or 777, 600 bytes, and it would be imperceivable, as each color channel would only be one bit different, like the difference in 255 and 254, you would not notice it. This assumes the image format preserves three channels of pixel information, like PNG.
ifell3 (11 months ago)
So someone gave me a photo and said do not release it, that had a jsteg in it, but then I wrote another jsteg to it, would it not over right the first?
Carlordau (11 months ago)
4:20 - captions - has a value of free. Got to love the accent.
Stewie Griffin (1 year ago)
great video
Stewie Griffin (1 year ago)
well done
Smail (1 year ago)
What if I make a screenshot and/or safe it as png?
Ben O'Neill (1 year ago)
Could the watermarks be deleted by randomizing the least significant bits?
Jay H (1 year ago)
1:45 Its not too useful I believe, since a simple hashing of the original and the new image can show there is a difference
אורי יגורוב (1 year ago)
Lol who made these captions? Looks like auto-captions
Romeo Santiago (1 year ago)
Watch my new video, friends...Geez. Facebook locked my boyfriend out of his account. Sometimes I felt that he suffered because of me. Because I was fighting the western intelligence agencies and he got involved... Sorry baby...Seems they were harassing him because they can't get to me... My poor boyfriend, got locked out of facebook for a crime he didn't commit. He simply liked my posts against the CIA. Is that evil? Well, I made this video to get revenge for you, my dear... https://youtu.be/ZvHcmXzxR4g
LPChip (1 year ago)
Awesome video. Can this be done with audio as well? I''d love to see a video about that.
TOMYSSHADOW (1 year ago)
Of course you could also paste a passworded ZIP onto the end of a JPEG in a hex editor and any photo viewer will ignore the invalid image data while something like 7-zip will detect and decompress the zipped data.
Badboy DCX (1 year ago)
Dark web
Rock & Rollin' Nolan (1 year ago)
6:53 Mmhhmm, I totally know what I'm looking at right now. I understand it all. WOT!?
John Smith (1 year ago)
Everytime I watch this guy I feel even dumber
Justin Tyme (1 year ago)
so NASA have hidden messages in their photos??
I have no clue what he is talking about
Liam Hopleyyy (1 year ago)
wuss poppin
Sam Nub (1 year ago)
From now on, I'm going to watermark all my image work with the tragedy of darth plaguis the wise
nilloc93 (1 year ago)
this was also done (with no level of subtlety) to distribute the 3d printer files for the liberator pistol
cooldude23407 (1 year ago)
I love what the letter says XD
A.J (1 year ago)
more examples less talking
FaRo (1 year ago)
I watched this video in fullscreen and my monitor has connection problems, so I thought you put a secret message into the video.
Paul Kreuz (1 year ago)
tsheantd imse cnouodlz!.
PangaeanConquest (1 year ago)
Digital Ash TCG (1 year ago)
What then happens if you screen shot a file with a message in it? is the message lost? covered up by other noise? Either in full or in part?
Philippe Carphin (1 year ago)
Subtitles are great "Stake in a graphic", and the best thing is that it never writes the same thing for jsteg : "chased egg" is my favourite.
Topher TheTenth (12 days ago)
Philippe Carphin: Why not "steak in a graphic" to complement your "chaste egg"?
Ashish Gupta (1 year ago)
how do you decrypt the message?
aspie96 (1 year ago)
Wait. Why in the steganographic image formed just by the last 2 bits could you still see the tree?
George Dimas (1 year ago)
Harley Moore (1 year ago)
You guys need a patreon
Christopher Derrell (1 year ago)
3's and 4's? Can you have fours with the 2 least significant bits?
Lars Martin Jensvoll (1 year ago)
The Norwegian police did this after the Breivik terrorist attack, with confidential images released only to the different attorneys representing victims and such. One picture was leaked to the press, and since the pictures were secretly watermarked they knew exactly who leaked it. The attorney was thrown off the case and lost his licence.
Alwin Priven (1 year ago)
the captions are so weird.
Djorgal (1 year ago)
I add random noise as steganography in all my images and only a select few have a meaningful message encrypted in them. Good luck trying to decrypt it all :)
DamnDesert (1 year ago)
That's an awful lot of work to just hide a message, think I'll stick to using file encryption..
Jason Myers (1 year ago)
you can hide gig's in images.
DeepSheet MissFeet (1 year ago)
idont understand machine learning. you just give it some training data and that's it. now you can detect Steganographic data which is designed brilliantly to bypass the statistical stuff .etc. how is this balanced.
kiwin111 (1 year ago)
Shubham (1 year ago)
Every time i change pixel value of an image using putpixel method in python.....it alters the image but next time when i check the same pixel value it shows some bizzare value....why isnthis happening
Talha Tariq (1 year ago)
ewwww das gai bai i unsubscribe :D
Talha Tariq (1 year ago)
Vendetta Vegan (1 year ago)
Wikileaks had an strange email with a load of photos of Antarctica in. this guy needs to look at them....
Vendetta Vegan (1 year ago)
Im actually a shill for the meat industry, Mmmmm bacon
Mayor Ushanka (1 year ago)
we get it, you're vegan
Hacking Vision (2 years ago)
Thanks I'm trying to learn stenography at the moment.
Nacho (2 years ago)
Does anyone know of a program that does this? I want to try it on my own.
backwardtelevision (1 year ago)
Nacho Keiniger openPuff
Sam Sırri (1 year ago)
Just search on softpedia
huB!erTi2 (2 years ago)
you look like peter parker
drditup (2 years ago)
You could do this with videos as well, and then you have the opportunity to perform transforms over time as well as across the image. But since I thought of it now, somebody has probably already done it. Is it something you could make a video of, computerphile ?
Raj Rajvir (2 years ago)
Can you please provide english subtitles. beacuse it is problematic for people to understand the accent and that too when you speak fast
oldcowbb (2 years ago)
thats how you find sombra
Christopher King (2 years ago)
Encryption is actually quite important. Otherwise, the attacker can just test the file to see if it contains a message.
Topher TheTenth (12 days ago)
Christopher King: not true: If a non-random string of digits (a message) is added (modulo 2) to a random string of digits, the output is as random as the random number that was added. Nobody can look at the output and see that it contains a message. Photographs are not random, because the world doesn't consist of molecules each of which has a color that is totally random vs. the colors of adjacent molecules. However, when the photograph is made into pixels, and each pixel is three integers (three colors) each of the three ranging from 0 to 255, the resulting sequence of odd and even integers IS totally random. So, when the message is added into that, the result is going to have the randomness of odd/even that the original photo had, and nobody will be able to detect that a message is in there. In any case we can assume that the message of 0s and 1s used to determine the odd/even sequence of the photo's color-value integers will already have been encrypted by other non-steganographic means.
jennifer siagian (2 years ago)
Wow Luke 8:17
someone give this guy some nerdy glasses :P
Bartosz Olszewski (2 years ago)
just hide data in dickpics, it would just be fun to know that people desperately trying to get the information have to look on dicks all the time lulz.
Sparse (2 years ago)
That.. is the nerdiest thing: 5:17
Jason Dashney (8 months ago)
Yeah, all I heard was the sound of Charlie Brown's teacher.
Khaisar (2 years ago)
lol right I don't understand this video what so ever :/
EdMcF1 (2 years ago)
But you can see a smile being suppressed as he is about to say it.
Wheelie Blind (2 years ago)
There is software that finds the hidden information so its not such a great idea, to use that as your only way to encrypt your message, and I'm talking about a picture where you cant' tell by looking that it has a hidden message in it, which is the best thing you can do, but I'd encrypt and compress the information using an other way first and then hide it in a picture.
Uncredible (2 years ago)
Can you share the software used to create the steganographic images?
zeezaa (2 years ago)
what if you do that in reverse? you change the bits of some other file and hide a picture in it
JNCressey (2 years ago)
What if you hide a picture inside another picture?
zeezaa (2 years ago)
+Weston Silbaugh multiple files continuing the message, like a music playlist
my dude (2 years ago)
you could hide an image in an audio file but it would have to be massive
my dude (2 years ago)
well if you did this with something like a text document and change the least significant bit of each character, the characters will be completely different and the document will be invalid. You could replace words with synonyms but the amount of information hidden will be quite limited or use leet speak but then it becomes obvious and still limited.
Emperor Spock (2 years ago)
3:08 Number 3: the larch. The larch.
Technicide (2 years ago)
Isn't 101101 a dollar sign in binary?
Patrick Last Name (2 years ago)
+TheMaskedVictini there are charts on the internet of the entire ASCII table
Technicide (2 years ago)
Oh, OK, thanks!
Fearleas (2 years ago)
Nope it's 45 in decimal and 45 is the character '-' in ASCII

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