Superfish has developed a new image search algorithm and deployed it via a browser addon for Internet Explorer and FireFox that allows you to find a product on any of several popular online stores and automatically see similar items from around the internet.  Unlike systems like Amazon, the similar items are based upon image processing algorithms that analyze the item on the page to present similar looking items, so you see similar shoes, purses or other items with the same properties as what you see.  In a recent blog post they discuss some of their technology:

Visual search for flat objects already exists, and it is not bad at all. For example, there are pretty good optical character recognition (OCR) and bar-code readers in use today. But we live in a three-dimensional world where objects take on dissimilar visual forms when viewed from different viewing angles. The same shoe looks completely different from the front, back, side, top and bottom. While even a young child can abstract a real-world object from its myriad appearances, computers can only compare images by their apparent features. Superfish employs algorithms that handle complex geometries to recognize an object regardless of the angle the image was captured.

The addon works for Windows & Mac, Internet Explorer & Firefox (no Safari, Chrome, or Opera support it seems) and is currently available in a “Beta” state but pretty functional.  Hit their site for a demonstration video and to download it.