A current trend among the art community is to collect and trade character designs on character repository websites such as Toyhouse.
For this, artists create character designs and put them up for sale or auction. These can range from individually designed, complex character sheets to an entire sheet of same-posed characters in different color schemes.
The buyer usually receives a high-resolution image as well as the right to draw the character or use them in roleplaying forums.
It is common practice among adoptable creators to define rules and terms on what the buyer is and isn’t allowed to do with the character (e. g. no re-selling), and place a text on the bottom of their auction stating “By bidding on this character you agree to these rules”. Many go so far as to threaten to reclaim the character if the rules are broken.
But is it really as legally waterproof as assumed?
Fortunately, the majority of the art community is very respectful and supportive towards one another, so usually the buyers abide to the creators’ rules. But, like everywhere, there’s always a couple of bad eggs. Therefore, as a creator, you cannot be careful enough if you put your intellectual property up for sale.
I stumbled upon an informative article on the subject of adoptable character purchase agreements that I thought I’d share. Unfortunately it reads a bit condescending, but the content appears to be well-researched.
I hope it helps!