PNG and Hidden Pixels

Re:PNG and Hidden Pixels by est on Tuesday September 01, 2020 @03:46AM (#24339460)

I remember there was a similar trick that hides data in GZip streams in its FCOMMENT block.

Could something similar be done with DEFLATE? Allocate some unused Huffman table? Put stuff in reserved bits?

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Re:PNG and Hidden Pixels by ekimekim on Tuesday September 01, 2020 @03:53AM (#24339496)

Specifically with PNG it has a concept of "private" chunks which you can use to store arbitrary data. Conforming decoders will ignore these chunks, and may or may not drop them if the file is modified. See https://en.wikipedia.org/wiki/Portable_Network_Graphics#%22C...

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Re:PNG and Hidden Pixels by 082349872349872 on Tuesday September 01, 2020 @04:11AM (#24339566)

A simple technique would be to use different block sizes.

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