We've built a search by image engine http://TuuSo.com, focusing on visual shopping from mobile phones: users can take a photo, and then search for visually similar items to buy; or web users can crop any photo, e.g. on someone's fashion blog, and search for the products s/he is interested in.

The TuuSo image search engine is as good as the best engine on the web. Our latest engine utilizing GPU can search 1M image in ~60ms with +99% accuracy.