I was at the Rijksmuseum, Amsterdam. Right as I got into the room pictured, a woman walked up and took a photo of this painting. It's one of my all time favorites. So I'm like, "Dude. She took a picture. That means it must be ok". So I grabbed my camera and did my big head big art shot. I tried to be a bit discreet by covering the flash with my thumb so as to lessen the impact.
A guard saw my little teeny flash and starting yelling at me. And that damn guard followed me around for the rest of my visit. I even explained that there was a lady who took a picture before I did, with a MUCH BIGGER FLASH, but that apparently was not the right thing to tell her, because she yelled at me more. I finally escaped to the bathroom, hung out for a while, and made my hasty exit once I was assured she did not wait for me outside the door.
Moral of the story? When taking pictures of art, well, just don't take pictures of great art, ok?