A few years back I found myself wanting to know where a digital picture originated and I found there were no tools to do such a thing.
Then came Tineye.com. They developed a search function that could identify parts of your image, the “likeness” if you will, and then compare it to other images on the Internet. By their own description “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. Our fingerprinting technologies have been developed by Idée Inc..”
It worked fairly well the few times I tried it. I found when looking for commercial images I always got the result I wanted. If I was trying to match a photo of a person or something more obscure I generally got nothing.
Then Google launched their reverse image lookup and soon integrated it into the standard image search and it worked REALLY well. Possibly because Google has permissions into more places and more powerful servers to cache and search existing images. You might have noticed when you search for images on Google there is a little blue camera icon now in the search bar, that is where you can upload your photo for the reverse search. http://images.google.com/
I think both of these services are limited by what they can peer into on the web. For instance, if you were sent a photo from someone’s Facebook page, but their profile or photos were set to private, I don’t think Google Images or Tineye.com can peer into those private accounts and match your photo to the one available in the Facebook profile.
One of the best things I’ve found about Google Images is that if you want to know where a photo originated you can do a search, then sort the results by date and find the oldest search result to get an idea of where it was first used and thus possibly find its origination.
Another great use is when you have a low res version of a photo and want something bigger you can search using the low res image and then sort the results or filter by image size in Google.
I’ve heard of people using it for dating purposes, someone you have found online sends you a photo and you can search to see where else that photo might appear…interesting possibilities there.
In all, these tools become more and more useful once you realize you have them at your disposal, you will think of reasons and ways to use them.