"The image's Quest"

I'll start with a simple scenario : There's this photo you downloaded a few months ago ... and now you want to find where it comes from (because you want to credit the person who took the picture, because you want to find the web site's url you took it from, because you want to contact the author or do a modification and want to make sure the author posted it with permission to modify ... )

What to do ?

The first obvious thing is to search the filename on any search engine (google, bing, yahoo, altavista, photobucket etc ...)

But assuming the filename can't help you - (either it's irrelevant or you saved it under a new name - so there's no way to get any clue from it)

Here's some of my suggestions :

Google is offering the feature "Find similar images" which is cool because you can direct the search visually, but in my experience I end up at best with a "close, but no cigar" situation  (this service was previously in the Labs section http://similar-images.googlelabs.com/)

Now if your picture is a .jpg inside your photo - there are more informations than you think (it's called Exif) and you could use that to narrow your search.

For example flickr.com is offering a search tool based on the camera model (it's called "Camera Finder")

There are also some "image search engine" with a twist, that could help you in your quest :

• www.kalooga.com specializes in finding image galleries rather than individual images
• www.picsearch.com
• http://elzr.com/imagery allow to specify filetype, color, size 
• www.pixsy.com video and image search

Alternatively some search engine like "retrievr" (http://labs.systemone.at/retrievr/) will allow you to either draw what you're looking for ; or (like TinEye) will allow you to upload the photo you have and hopefully find where this photo appears!

And in last resort, if all else fails, there is idthis.org where you can post your photo and hope that a viewer will give you a hint, or advices that will put you in the right direction.

Now, if you have other tricks, your comments are welcome ... I have this pesky photo downloaded 2 months ago and still can't find it's source... (I wish, the source url could be automatically embedded in  pictures).