Distrobooru

Okay, imagine this: a website for image board image collectors that is just basically a big dictionary of image hashcodes and tags for the images, but which doesn't store the images themselves  so it doesn't have to worry about bandwidth.   Programs on your computer could tag images you have, and download tags from the site so that, like with danbooru or flickr everyone (supposedly) helps to organize the collection.

Does something like this exist?  And if not, why not?

>>1
If you can be more specific i can create something like this.