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