Some weeks ago someone pointed out that the links on the ICRA website to register for the Digimarc adult content watermark were broken.

I contacted someone at Digimarc, and the links are now active again. You can register and receive a unique watermark ID which will invisibly mark your stills as containing adult contentm so they will not display on content-filtered browsers. We have been using it for about 2 years now.

The registration and the plugin to use it are both free. The plugin works with Photoshop and anything that is Photoshop plugin compatible. I use it with Thumbs Plus, there are some other applications out there that are Digimarc compatible as well.

The link is

http://www.icra.org/pkd/