It's more complicated than a hash, but who knows what their proprietary engine uses. Here are some guesses. https://www.quora.com/What-is-the-algorithm-used-by-

It's more complicated than a hash, but who knows what their proprietary engine uses. Here are some guesses. https://www.quora.com/What-is-the-algorithm-used-by-Googles-reverse-image-search-i-e-search-by-image https://www.quora.com/What-is-the-algorithm-used-by-Googles-... Regardless of how that process works, once Google scrapes an image, they can store some metadata similar to the output of your software, so that it may be used for sorting the much smaller set of images returned by the image similarity algorithm. The top result can then be deemed the "most original" image since it contains the most detail, and the webpage it was found on can get a boost of pagerank or something.