Scott--
Also, since you said blog: many bloggers only hotlink out of convenience. Also, because Getty sends letter to hotlinkers (like me) we know that at least as far back as Nov. they either weren't checking the html to see who hosted the image. So:
1) If you still can, figure out if you hosted the image or if you only hotlinked.
2) If you hotlinked, breath a sigh of relief and look for posts discussing Perfect 10-- because the 9th circuit in the US ruled that hotlinking was not copying or displaying under the US copyright law. (Whether the Supreme Court would rule the same we do not know, but the 9th circuit is one level below that. ) But if you can, get proof you hotlinked. Identify the site you hotlinked from. Keep that info available and pause before writing up your defense. (It's nice to decide on things with a clear mind.)
3) If you hosted the image on your server, do not volunteer that information because Getty may not have any proof you hosted. Do not volunteer it here; do not volunteer it in a letter to Getty. If they don't have the evidence, let them guess. If and when you do write Getty, ask them to show you html underlying the page with the screen shot. The html would be required to prove your display involved hosting the image-- not hotlinking. They may not have it. In that case, they can't know for sure whether you hosted until discovery-- because you aren't going to tell them. right?