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The problem:

An artist posts an image of their work online with a creative commons attribution licence (on site A), someone reposts the image with attribution on another site (site B), the internet happens and the image has been cropped resized and the attribution notice is lost.

The (tentative) solution:

The artists name, web site and attribution licence is steganographically embedded into the image. So consumers of the image or web sites who host these images can pull out the data (and display it).

The question:

How would I go about steganographly embedding data into an image, that will be resilient to resizing and cropping?

Things not to worry about:

  1. Tampering of the data
  2. Just using exif metadata (as that is often lost)
  3. Convincing all the artists they should do this
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This is a big research field with a lot of different techniques. The right term here is "watermarking". Similar to steganography but with different requisites: we hide only a mark and we want to be resistant to cropping, resizing and others (blurring, compression, noise addition, ...). One approach to resist cropping is to copy the mark several times in different positions of the image. One approach to resizing is to hide information by modulating the DCT coefficients.

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  • $\begingroup$ Do you mind expanding on what you mean by: DCT coefficients? $\endgroup$ – DarcyThomas May 12 at 2:30
  • $\begingroup$ JPEG images are compressed using DCT (Discrete cosine transform - en.wikipedia.org/wiki/Discrete_cosine_transform). In data hiding applications using JPEG images is usual to modify the value of the DCT coefficients. $\endgroup$ – Daniel Lerch May 12 at 21:17

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