Currently there are eleven attributes for the img tag, two required and nine optional. Frankly the tag is already bloated enough that I don’t think one more attribute is going to matter. Something as simple as lic="license-abbr" would do wonders for image rights on the web.
Not only would a license attribute help image search engines, it would help protect copyrighted works by drawing attention to the fact that they are copyrighted.
Interestesting discussion going on at this site around the potential possibility of implementing a license attribute into 'img' tag.
Sounds pretty reasonable and simple to implement. Will also help solve a whole heap of other problems. Keep an eye on it as good basic sense to implement and worthwhile if you sell/license your content.