Is there any open source code/library that can find similar images like TinEye does?
There is the google serach api http://code.google.com/apis/imagesearch/ but it is Deprecated. But that doesn't mean that you can't expect a replacement. Also doesn't meant there will be.
Yahoo also has one here
http://www.programmableweb.com/api/yahoo-image-search
Those are free. I would expect the yahoo one to stay up.
Hope that helps. Cheers -Jeremy