Is photography not allowed in theaters?

I believe so, but I don't know exactly what the rules are. Camcorders (videocameras) are definitely not allowed, but I'm not sure about regular cameras (cameras which only take still pictures).

Whatever the rules are, they don't seem to be strictly enforced (at least, at regular movie screenings). For example, they don't search you, to see if you have a camcorder. Also, most cell phones nowadays are also cameras -- most of them at least take still pictures, if not videos (although the picture quality is usually sub-standard). But they don't take your cell phone away before you enter the movie.

At premieres and advance screenings, the rules are usually more strict. I have a friend who is always getting tickets to advance screenings, and whenever we go to these advance screenings, there are always security guards outside the theater doors, who make us give them our cell phones (unless they are the kind that can't take pictures). You have to give them the phone, and tell them your name. They write your name on a Post-It note, and attach the Post-It to your cell phone. When the movie is over, you show them a valid ID card with your name and picture, and you get your phone back.

However, even at these advance screenings I've been to, the security guards still do not search you. They don't search your purse, for example, to see if you have a videocamera stashed in there. They actually don't even search you to see if you have a cell phone. You can lie and say you don't (but often, the people who lie have their cell phone in their back pocket, or shirt pocket, and the guard will go, "Hey, you're lying. I see your phone. Give it up.") But if they can't see that you have one, they can't search you to be sure.