CODEWITHSUNDEEP
iphonexcodeimagefilemetadata
SolidSnake4444
SolidSnake4444

Reputation: 3587

How does one embed a file inside of an image? iOS iPhone

There is an app on the app store called active photo (http://itunes.apple.com/us/app/active-photo/id366798464?mt=8) that allows you to embed a hidden image or .exe file inside of an image. I would like to know how to do this regrading adding images to images, kinda like sub images in the original image.

I've been looking into metadata but no tag seems to be big enough to hold an NSData representation of the second picture.

How would one go about adding any type of file to an image, either through embedding or metadata, that would allow the image to be sent though email and or text message and still retain the data?

Thank you.

Upvotes: 0

Views: 848

Answers (2)

Shepard
Shepard

Reputation: 811

I don't think it is possible with JPEG because it's a lossy compression so you would end up corrupting the embedded file. But PNG uses a compression method similar to Deflate, which is loseless.

I have started writing a program like this. The idea was to hide bytes of data by splitting them into the least significant bits of pixels' color channels. Let me do some examples.

An RGB-8 image represents a pixel with 3 bytes, one for red, one for green and one for blue. I store 3 bits into red channel, two into green (human eye is more sensitive to green color) and 3 into blue. So I embed one byte per pixel. Similarly with RGBA-8 image I do 2-2-2-2. This of course involves some bitwise operations.

Things become more interesting with RGB(A)-16 images, where there are two bytes per channel. I use the entire least significant byte of every channel with minimal distortion (worst case 255 / 65535 = ~3.9%) and store up to 3 or 4 bytes of data per pixel. Not bad!! Moreover there are no complex bitwise operations in this case, a single assignement does the job.

There are lot of improvement to it. I thought to ask the user a password, hash it and seed a secure pseudo random number generator, then no longer move pixel by pixel but instead asking the generator for a new random index.

The drawback of this solution is that the more data has already been embedded, the slower it becomes, because the generator will give more and more occupied indices. But it is much more secure in this way. To make it even more safer I thought to introduce noise data in the untouched pixels, in order to hide the positions of the true data.

As you can see you can do a lot with PNG images! If you are interested I can give the code I wrote so far.

Upvotes: 0

ravuya
ravuya

Reputation: 8756

This is known as steganography.

I would imagine the simplest way of hiding a file inside a JPEG image is just to alter its pixel data in such a way that the compression doesn't damage it but is subtle enough that an interceptor can't detect the hidden data.

Upvotes: 2

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