You could be fined $30,000 per case if you post a picture with out citing the source. The goal is to fight child porn, by making it possibly to back track to the source of the image, but the requirement would apply to all pictures, not just porn.
On one hand, it would be nice to be assured I would be credited for images I take, but on the other hand, $300,000 seems really steep, and if people are violating the law by having and making child porn, what makes you think they will actually credit their sources or just put bogus credits in place?
I suspect this is another case of congress not grasping technology and mentally flailing their arms.
If there is a requirement to cite the sources of images, will you stop positng images? Claim they are all yours? Claim they all magically appeared on flikr? Ignore the law?