<i>All images where hosted by a 3rd party, I have never hosted any copies of the images in question</i>
If you are in the US, that's pretty much the end of it. Getty cannot win in court. Mind you, if you engage, they'll likely send you something that claims they could. They are wrong.
What you should do depends on whether you want to position yourself to make a strong case to the Washington State. DA or not. Since there is no way they can really win in court you could just ignore them. Do nothing, no complaints to the DA etc. Alternatively, you can respond, cite Perfect 10, and wait to see their counter response. If they continue to threaten you after citing Perfect 10, send all the correspondence to the Wa. State DA making the case that these guys continue to press when they know perfectly well the courts have ruled against hotlinking being a copyright violation.
If my case wasn't so stale, I'd write a complaint letter-- because I was in a similar position to you. Unfortunately, I didn't think of it at the time, and Greg came around with this idea a year and a half later. But people do need to write letter emphasizing that:
1) Getty is certainly aware of Perfect 10, and yet sends out letters for hotlinked images. Checking for hotlinking is trivial, they merely need to look at the url. Either they don't check which is very bad or worse, they send out letters knowing that the url corresponds to hotlinking. Given the tone of the letter and the monatary demand, this is a very unethical practice.
2) Even when people respond with Perfect 10, they sometimes reply back not accepting that as evidence that the images was not hotlinked and continue to request money. (At least they did this with me. If they've stopped, that would be good.)
But really, you are in a strong position to complain even if only (1) occurred. You would be able to write a stronger complaint letter than *most* people who complain. (It is an unfortunately irony that the people who have the strongest complaints against Getty are often so relieved when they discover they are free and clear that they don't write the letter of complaint. After all: problem solved! But really, it would be nice if the hotlinkers did write. I wish I had. But it would be a bit silly at this point. Though.. I dunno. Maybe I should anyway.
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