Looking at articles on digital art I thought how to verify whether one image is equal to another, visually similar, so no matter your copy, PNG, JPG or frame in a video, verify if it is really different.

There are programs like pyscenedetect, Shotdetect that detect the great changes in a film and programs like ffmpeg or mplayer that export hash and md5. This serves to see if a frame is exactly like another pixel per pixel. But if they are very similar it doesn’t work properly.

My idea is to reduce every image to 8×8 in gray or few colors and cut the colors to a few or white and black so that you have a signature of the image.

For example:

convert image.png -compress none -resize 8x8\! -compress none -depth 3 ppm:- | md5sum

This is limited, but you can verify similar frames with quite precision.
It can also be preserved as a ppm image which allows a visible version of the frame, similar to a QR or a digital signature of the frame.

This is for an idea that I’m working on making RSA-based cryptographic art.