I have the impression that in Muslim countries taking pictures of people is often not welcome. On the other hand there are other countries where people really enjoy it (and also sometimes expect some money). In which places in the world (countries, cultural regions) is it considered offensive when a tourist takes a picture of local people?
Also should you always ask for permission or does it depend on the region/situation?
Always ask before taking a photo - unless they won't know if you take it. That's not supposed to sound creepy, but sometimes you're say, taking a photo of the Eiffel Tower and someone happens to be in the shot, so that's fine.
NEVER pay money for a photo. It encourages begging, or harassment. Ask permission, and if they say no or want money for it, offer instead to send them a copy of the photo, or show them the photo and ask if that's ok. Thank them and move on. I realise this is a controversial one, but personally I'd feel really strange asking for money if someone wanted to take a photo of me, so I treat others how I'd want to be treated.
Susan Sontag who wrote "On Photography" (1977) had this to say:
"The camera doesn't rape or even possess, though it may presume, intrude, trespass, distort, exploit, and, at the farthest reach of metaphor, assassinate - all activities that, unlike the sexual push and shove, can be conducted from a distance, and with some detachment."
In most places, taking a photo in a public place is fine and you have the right to do so. It's in private places (homes, schools, gyms, workplaces) that you don't have the right and must have permission. However, what you DO with the public photos can affect your rights - for example, newspapers can publish news photos and don't need permission. However, try and sell a picture of a person on a photo website or similar, or use it in a book, and you'll need permission to use their image for commercial purpose.
Of course, how are you going to get permission from the awesome old Cambodian guy with the crazy beard that you got a travel photo of? Good question, and I've met several travel photographers who consider this a grey area and just risk it. But the key word there is "risk".
I'm not certain this should be down to country or culture.
I don't think the UK has a culture where people object to having their picture taken (*) - we have the highest number of CCTV cameras per head of any country in the world - but I for one would my very displeased if a stranger took my picture without asking.
And for those cultures you mention where people would expect money, asking them would also be a good idea.
(*) but some locations are off-limits to photographers, so while you may not offend someone, you may find a policeman or military guard coming to have a word if you photograph things that might be terrorist targets or military bases...
In addition to cultural issues, one should also consider that taking photos of border crossings, military installations, some police stations, and their associated personnel may be considered spying in some countries, and carry a VERY long prison sentence.
