I think color images, as opposed to mapped, would be the way to go for steganography. More room, and nobody expects them to compress.
Yeah; but even if we're talking full 24-bit images, we're going to have problems. Once 24-bit displays become standard, I really doubt that there will be many images stored in a non-lossy format. And once you try to hide data in a lossy encoding scheme, you run into a lot (though not all) of the problems you have with colormaps. It would be a lot easier to hide data in an image if one had a control-image (the original) as well as the altered-image (the one holding the message), but this defeats half the niftiness of trying to do things this way.
Eli ebrandt@jarthur.claremont.edu
-J.
And once you try to hide data in a lossy encoding scheme, you run into a lot (though not all) of the problems you have with colormaps.
I think it's even worse... with unlossy compression, you can frob the uncompressed bits and just lose compression. With lossy, you can't do that, because your message will be smeared away. And frobbing the compressed stream will produce ghastly artifacts. But not all images will be lossily compressed. I find that JPEG, for example, usually introduces too much gunk to be useful. Certainly, sending an LZW TIFF should be above suspicion for quite some time.
It would be a lot easier to hide data in an image if one had a control-image (the original) as well as the altered-image (the one holding the message), but this defeats half the niftiness of trying to do things this way.
Yeah, this is just a cheesy OTP. Not much point, really. I've been thinking about the GIF case; the "optimize for colormap cyclic continuity" technique looks like it will produce better images than the "crunch to 128 colors". Since I have to write some annealing code for a neural-net trainer, maybe I'll repackage it for colormap optimization and see what the results look like. If you wanted minimum visible crud, you could start with a true-color pic, find the colormap, order it, and dither down -- rather than adding white noise to pre-existing dithering. You know, I think I've been taking the graphics-weenie approach to this. Who cares how the image looks? Who cares if it's even an image? Just take your damned PGP file, ^=0xff it, and rename it "hotbabe.gif". uuencode and mail. The NSA is not going to be viewing every picture you send, I hope. This fails on "plausible deniability", I guess.
-J.
Eli ebrandt@jarthur.claremont.edu
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Eli Brandt