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Comment by auxym | Hacker News Reader

If the hidden data is encrypted anyways, then wouldn't it be indistinguishable from truely random data? What would then be the point of distributing it randomly or in order?

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Actually, the thermal noise of a camera is biased so a uniform random distribution of low-order bits will be easy to detect. You need to preserve as much of the thermal noise as possible and try to choose pixels from high frequency regions of the image (where the thermal noise is harder to separate from the image itself).

So maybe the best approach would be to use a filter/transformation to exclude hard-lined regions (edges) and only embed data within variations/gradations?

Other way around: edges are a good place to try to hide stegotext because of the high frequency components (the edge effect, which is also why JPEG artifacts are worse along sharp edges).

If the cover image is a solid block of colour, you can detect the presence of the steganography by noting that the first N pixels vary slightly, and the rest are solid.

Similarly, if you have a clean reference of the source image, you could observe that the first N pixels are modified and the rest are not, and conclude that something is hidden in them.

If the pixels are selected at random, this analysis is less conclusive. Ideally you'd hide a random value in every pixel so that all pixels are manipulated equally.

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