instead of using a hash to find images you should use a lower resolution version of same image to find the full resolution version. even Bing image search has a feature where it will automatically show you different "image sizes" for the same image, for example the following are different sizes grouped by Bing a truly smart system wouldn't even save the image but simply find the highest quality version of it on the web and save just the address. i tag @fiatjaf because he appears to capable of understanding my brilliant ideas.