[freehunter]

Problem is, copyright is implied on the part of the creator. It does not need to be applied for, nor is there any requirement for a copyright notice.

Just because you didn't watermark your image doesn't mean the copyright now belongs to Pintrest (or imgur, or Google+, or Facebook, etc) because people who didn't hold the copyright and didn't have the standing to give it away posted it.

[icebraining]

And that's why you can send a DMCA takedown request and they'll have to take it down. I fail to see the problem here.

[anothermachine]

the watermark isn't for legal purposes, it is for communication and content-devaluation purposes

[aiscott]

This is true, but if you want to receive statutory damages for copyright infringement, you have to have registered your copyright.

http://www.copyright.gov/help/faq/faq-general.html#register