This is an interesting article on taking pictures in restaurants. It also features some comments by chefs we really respect - especially Sean Brock.
We have never hesitated to take pictures of our food. We try to do it quickly and without a flash. We never really thought that a restaurant might not appreciate it.
I will add that we will try to take pictures of all the food we review, but I also want the readers to realize that the pictures are there to add to the description, but we are not professional photographers. If we say the food looked and tasted good - it looked and tasted good. If the picture doesn't look good to you, it's probably a reflection of our lack of skill with a camera, and not a reflection on the food.