Yeah, you're right, I don't think it can actually have a virus, they are actually .exe files, and only Windows can be 'tricked' into confusing an .exe as a JPEG. My mistake there. I don't see how the iPhone would be dupped like that.
So maybe it's just the anti-virus looking at a file, and thinking there might be a virus.
What anti-virus is the OP using?
edit: regarding jpeg viruses:
http://www.secureworks.com/research/threats/jpegvirus/
Didn't quite understand if that report had something to do with dupping windows to think it was a jpeg file, or if it was really a jpeg, that took advantage of some vulnerability when reading the file (hovering with the mouse accesses at least the metadata)
edit2: also, sophos has previously showed you can have JPEGS that execute code, but you'd first have to have 'installed' a virus (.exe file), that will then run the code present on the JPEG file. So you'd have to be infected first. Maybe he has such an image? (speculating is fun!)
http://www.sophos.com/pressoffice/news/articles/2002/06/va_perrun.html
Message was edited by: jinx.pt