"Strict liability" laws are laws to which there is no defense if you break them. For example, if you are hauling gunpowder and it blows up and damages property or a person, you are often strictly liable - no excuses - because of the risky nature of your undertaking. That's a strict liability tort, or civil claim. Another common one is statutory rape. If a person over the age of 18 has sex with a person under the age of consent they are guilty of statutory rape, even if the girl consented, even if her parents consented, even if her and her parents told you she was of legal age, none of those excuses matter. All the law cares about is her age and your age, that's a strict liability crime.
In the realm of copyright law, copyright infringement is a strict liability claim. That is, if person A can prove that he created a work of art first and that person B then used or copied that work of art then person B has infringed in person A's copyright. It is not a defense to say that Person B did not know Person A created the work or did so first. It is not a defense to say that someone else told you that they owned the rights to the work and that it was OK for you to use it. Even a mistaken belief that
you created the work originally yourself, is not a defense. For example, look closely at the recent news about Coldplay being accused of copyright infringement over its hit song "Viva La Vida." Acclaimed guitarist Joe Satriani has sued Coldplay saying the song is so similar to one of his tunes that it infringes on his copyright. Coldplay's music representative were the first to comment and said "its purely coincidental that the songs sound alike" Well that was a stupid comment to make because thats not a defense to copyright infringement. George Harrison learned that the hard way years ago when a judge found him liable for damages for copying the melody to "He's So Fine" and using it for "My Sweet Lord." The court found that he did not intend to infringe, that he came up with the song of his own talent and creativity, but that it nevertheless infringed on the earlier song's copyright. Now Coldplay's lawyers have released a statement saying that Satriani could not obtain copyright protection for the song because the basic melody line that both songs share is not original - that it came from even earlier works and a cannot be copyrighted. That's about the only defense they got and its a stretch. I bet that case gets settled.
Getty relies heavily on the strict liability nature of copyright law in its letters and settlement posture. But it is misguided for several reasons: first of all, how someone infringed may not effect their liability but it can effect how much damages they pay in cases where Getty is seeking statutory damages. Think of the statutory rape example I gave above. Of course a judge will sentence a defendant more lightly if the defendant had a good faith basis to believe the girl was of age. secondly, Getty may have trouble proving it has exclusive rights to the image. Many folks are coming to us who got the images legally off of photo CDs for example; others have shown that the photographers have allowed their images to be sold on more than one site. Third, there are some exceptions to infringement -"fair use" is the best known example - but courts also won't award damages for de minimus or minimal infringement. Many businesses are getting Getty letters for an image or two used to decorate one small part of a multipage website or where someone has used only a part of an image to create a banner.
So while Getty keeps declaring that folks should "abandon all hope ye who enter" as there is no defense, you see from all of the foregoing that that is only partially true and that there may be full or partial defenses to Getty's claims.