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Learning a bit about IT security, a segment of the material was the basics of steganography - specifically, hiding information in the lowest significance bits of images, and converting images into sounds. For the first it occurred to me that many sites compress user-uploaded images, effectively destroying any information hidden this way.

My question is, are there techniques other than changing lowest significance bits that survive image compression, but aren't clearly visible?

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Yes there are, the techniques are often used more for watermarking but can also be used for steganography.

One such technique is placing messages in frequency space via a 2-D Fourier Transform. Depending upon various details of the way it's done, it can survive degrees of compression, resizing, and cropping.

Here is an example:

Baseline

Baseline

Stego-1

Stego-1 added to baseline image

Stego-1 FFT

FFT of Stego-1

Stego-1a

Stego-1a Recompressed Stego-1

Stego-1a_FFT

Stego-1a_FFT

Stego-1_resized

Stego-1_resized

Stego-_resized_FFT

Stego-1_resized_FFT

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