I was wondering how does tineye carry a search. Does it store all the images and then extracts exif data? Which in turn must be stored in a database and queried against. So probably it is using some sort of keyword/pattern matching algorithm...
The TinEye FAQ reads:
When you submit an image to be searched, TinEye creates a unique and compact digital signature or 'fingerprint' for it, then compares this fingerprint to every other image in our index to retrieve matches. TinEye can even find a partial fingerprint match. Those fingerprints use only the image itself, and not its name or surrounding text. Our fingerprinting technologies were developed by Idée Inc.
TinEye does not typically find similar images (i.e., a different image with the same subject matter); it finds exact matches including those that have been cropped, edited or resized.
Chasing this then to Idee and a google patent search for "idee image search" brings up a number of patents (mostly named "Methods and Systems for Content Processing").
While my digital signal processing background isn't there, these patents do appear to be similar to what TinEye implements... or if not specifically licensed by TinEye, do similar things with other algorithms that accomplish the same end (many of the results appear to be referencing things that TinEye does). The patents are much larger than those I have glanced at before - some reaching over 100 pages.
Unfortunately, neither of the founders of Idée, Inc. come up in the patent search - which is often a valid approach to finding the patents they started with.