I’ve always been a museum nutcase. Excursions to museums was a favorite during my grader years. I must have liked it so much, because, now, I would try not to miss visiting a museum if time allows. Museums are like banks that holds treasures of history, and creativity for me. It houses artifacts, and are home to masterpieces from famous artists of their time, and of ours. It’s kinda like a structure that contains the past in the present, and preserving them for the future. And other museums are now interactive. More than a place for learning, it is also entertaining, and engaging. But do you ever wonder why some museums do not allow picture taking inside? Don’t you just hate that?

Taking pictures inside some museums is prohibited for some reasons. Some, and not all museum, a certain area, or specific artifact/s may have high restrictive photo policies because:
1] Intellectual Property. Some museums have very specific intellectual property rights agreement with their donors, and lenders. These museum is to provide the restrictive policy, and it is easier for them to carry it out to an area, or gallery, or the whole museum as a no picture taking area to safeguard their contract.
2] To Conserve the Artifact. A rule of the thumb: Never take photos of paintings. Whether if it be oil, watercolor on canvas, wood, a sculpture, or what. And also on artifacts that has surfaces that are sensitive to light exposure. Ahem. The very same reason behind why museums keep a low lighting, or those fancy light fixtures that are not directed straight on or to the object.
3] Revenues. Museums has a way to control distribution of an image of an artifact through their catalogs, or postcards at their gift shops. A friend once asked me, why I bother buying him a postcard when I can get a picture if allowed. Keeping the postcard industry, and getting the Oh! Mr. Postman something to do are two of the other reasons that I do.
4] Prevention. Some may be done with a purpose to do harm, to reproduce, or other motives than just to take a souvenir shot. Hmmmm.. I know. I think I may have watched too much museum-breaking films. 
5] Causes Traffic. The more you loom over the art, the bigger the crowd that you seem to have formed. Maybe you have not noticed, but you’re not the only one inside the museum. And yes, they are paying visitors too. And no, they do not have the whole day that you may have.
6] and Lessens Art Appreciation. I like guided tours when visiting a museum for this reason because one might miss important details on an artifact, and it would be nice to have someone point it out for you. The more time we spend adjusting our camera settings, the less we try to pry on an objects details, and less time to study, and appreciate them.

So, okay, if you can take better photographs, and okay if you can work with low lighting, without flash, and still get an awesome shot. I get it. You must be one of those talented people out there. But with all due respect to the museum industry, or the postcard business, and your, uhm, credibility should those shots be seen by others who know better. It is always smart to ask if it’s okay to take a shot, or be sorry, and be called for because of ignorance.
There have been cases, when invited as a blogger versus than just a random traveler checking out the museum that photographs were allowed to be taken for documentation purposes. I have been lucky to visit a few museums lifting the restrictions and allowed us to take photographs inside, and around the place. And believe me when I say, how the little kid in me jumps around like crazy every time. If you happen to be lucky like that — still take the flash off, limit your shots, and, nicely, ask to what areas are allowable.

+ Ask if it is allowed to take pictures, or what areas are prohibited or restricted.
+ You can take a souvenir shot in front of the museum building or facade, or at the lobby. Most museums have a photo wall that are good backdrop for your souvenir shot.
+ They do have pamphlets with museum information. Usually I just take a picture of that one, and put it back. I do not what more papers stacked up, and getting those only increases their production demand for it. Unless they are useful for scrap booking, a photo of it is good to go.
+ Do not let photo restrictions stop, or hinder you to enjoy the museums! Come on now.
But most of the time —  like when I am traveling alone, and have no one take a photo of me — I aim the camera down and take a photo of my feet, and of the surface I am on when I  find myself in a museum where taking pictures is not allowed.