You might want to follow the issue of orphan works via the following site:
ASMP
It has a sample letter that speaks to the subject - I believe that the orphan works bill is not very high on congresses plate right now (the real push came when the GOP was in charge - there are other priorities now).
This whole idea of orphan works is why I suggest that everyone embed a copyright notice in the proper fields on all of the images they put up on the net. I also put a copyright notice on all of the images themselves - I do try to keep it subtle, sort of like paintings, when the artists name dominates the painting/image - it is an ego trip.
There are several tools that allow the embedding of copyrights into JPEG's, TIFF's, PNG's and other image formats. The only thing you can not embed the copyright notice in is RAW - since virtually all software capable of reading RAW, will not write back to the original media.
To protect yourself, embed your copyright - then the burden of finding you is up to the entity that wants to use your work. If you can demonstrate that the original had a notice and it was edited out - then you can go to town on their dime.
PDL