You do not have to ID the driver, but you will come under a LOT of official pressure to do so - from the court clerks, from the police, and even from some judges.
If the picture of the driver was good enough so that a judge can see, without a doubt, that it was not you, then your best bet is to go to court. But when you see the judge, you have to be very careful about the wording you use to tell him it was not you. If you say something that he thinks is testimony, then he can say that you have given up your right to NOT testify, and insist that you must now tell him who it was driving. (I am sure that the judges who visit this forum are gonna jump all over me for this one!)
Google "red light camera ticket" for much more info.
Pug