This project is to help the Internet Archive find duplicate images for their many images (particularly music album art covers).
Thanks to http://www.hackerfactor.com/blog/index.php?/archives/432-Looks-Like-It.html for the Simple Hash and pHash (aka perceptive hash, which uses DCT)
- MD5 checksum (This may change to SHA.)
- Simple Hash
Scale to 8x8, greyscale, hash based on above/below average - DCT (Discrete Cosine Tranform)
Scale to 32x32, greyscale, [DCT](https://en.wikipedia.org/wiki/Discrete_cosine_transform), hash based on above/below average excluding top-left "base" value