TinEye Reverse Image Search
Boing Boing just used this search engine to find the real photo for the Borneo monster, From the faq:
TinEye is a reverse image search engine. You can submit an image to
TinEye to find out where it came from, how it is being used, if
modified versions of the image exist, or to find higher resolution
versions. TinEye is the first image search engine on the web to use
image identification technology rather than keywords, metadata or
watermarks. For some real TinEye search examples, check out our Cool Searches page.