What is the rule if I have a photo of a person (whom I do not know) and I wanted to put it on here? (I know the answer is buried somewhere in the site rules-- can't find). It's a great photo of a guy just riding the train, but I don't want to cause any problems
hmm.. I put him on here anyway. I've got a print "train ride" that I took of some guy on the train today. Didn't really even mean to take him, but I really like it, and thought someone else may too. I'm sure he will never know
Although it may not be directly related to the question at hand, this is an interesting read. The author's book might also be worth getting (although I personally haven't done so yet.)
You can use a photo of a person in a public place, taken from a public place, for personal/educational/journalistic purposes (like DPC), but may not use it for commercial purposes without a model release.
The exceptions would be places where a person has "a reasonable expectation of privacy"--no cameras in public toilets, changing rooms, etc. The beach, the sidewalk or a park are fine.
I printed out that PDF EddyG posted a link to and keep it in my camera bag.
The REAL answer to this is that you can take whatever photo you can get away with taking. You can't legally sell anything of a recognizable person without a model release. You also don't have much to worry about 90% of the time if you do. I take a LOT of street photog and candids - the only problem comes if they find out you are selling them (unlikely) and want their fair share.
You can use it commercially if the person is not recognizable. I used the composition and some cropping to eliminate that problem here. I shot that with the camera held down at my waist, while facing about 90 degrees to the right as if considering a shot of the ocean.