[sowbug]

That's not really DRM. At best it's DRE (digital rights expression, a term I just made up). DRM controls the computer showing the content.

The problem with the idea is that it works only if every single photo/video player in the world agrees to respect the metadata in the file, _in spite of the wishes of the owner of the computer running the player_. Be careful what you ask for.

In theory, adding a copyright notice to EXIF is just as effective -- though everything is already legally copyrighted the moment it's fixed in a medium, regardless of notice. So you already have what you're asking for, and you can see how well it's working.

See also RFC 3514.

[tormeh]

That's a strawman. The classic DRM solution is to create a new format with some secret knowledge required to play it. Only players that respect the metadata are given the secret required to support the codec.