Originally posted by Parallax If patents and copyrights are not jealously defended by the holder, they become public domain. This is why you hear of stories like Disney suing a mom-and-pop grocery store for having a picture of Mickey Mose eating a doughnut painted on their wall. If they don't defend it, they loose it.
Copyrights do not have to be defended and items do not become public domain due to lack of enforcement -- ever. They expire when they expire, according to the various laws. (
http://www.copyright.gov/circs/circ01.pdf)
Patents also do not have to be defended to remain effective. This is part of the problem with patent trolls -- they buy up patents that weren't defended and are in general use and then try to sue everyone. Reform is much needed here. (
General Information Concerning Patents)
Trademarks, however, DO have to be defended. If you do not defend it, it is considered abandoned. Unlike patents and copyrights, trademarks are based on use, not registration. Underwood's devil was trademarked in 1870, and is still in use and still valid for that reason. Disney has
trademarked Mickey Mouse, hence why they aggressively pursue violations. Films featuring MM, however, are copyrighted.