"My [website use, posting, whatever] is 'Fair Use' so I haven't violated copyright"
"Fair use" is a legal "defense" to copyright. It was created to allow use of copyright material for socially valuable purposes such as commentary, parody, news reporting, education and the like, without permission of the copyright holder. A typical instance would be a brief quotation from a book as part of a book review. Uses allowed by "Fair Use" are normally a small part of a work and include an author credit and attribution. Fair uses are generally for non-profit purposes.
Fair use is rarely allowed where the use competes directly with the work or harms its commercial value.
Most fair use situations involve text. It is difficult to imagine any situation involving the Internet where someone copying a photo could claim the fair use defense. In typical infringement activities, such as unauthorized posting to Usenet, stocking websites from Usenet trolling, scanning from Playboy magazine, or simply copying from other websites-the fair use doctrine does not apply. Because the pirate is taking 100% of the work, not acknowledging the creator, hurting the work's market value, competing directly with the creator or licensed users of the work, and for other reasons.
So if you are a photo pirate, do not even think about the fair use doctrine. In your context it is a myth. Your lawyer will laugh at you, and the judge might not have a sense of humor where thievery is concerned.
