The fourth factor [the effect of the use upon the potential market for or value of the copyrighted work.] measures the effect that the allegedly infringing use has had on the copyright owner’s ability to exploit his original work. The court not only investigates whether the defendant’s specific use of the work has significantly harmed the copyright owner’s market, but also whether such uses in general, if widespread, would harm the potential market of the original. The burden of proof here rests on the defendant for commercial uses, but on the copyright owner for noncommercial uses.
Hmmm, does this mean the criteria is less stringent for a blog like this that has no ads and doesn’t take contributions than it would be for a blog making $5,000 a week from BlogAds? Anyone know?
If I copy a graphic image from a photographer’s site to my blog, then it then gets blogged everywhere to the point that sales for his artwork drop, then my copying would almost certainly not be fair use. This seems much more obvious when copying artwork, but applies just as much to the written word too.