the dipweed advice is an excellent summary. this also is not legal advice.
in general, if you are in a public place (that anyone can go to) photographing anything that anyone else can see, you are ok. things change if you are on private property, or taking photos of restricted subjects, or have some malicious/abusive/ridiculing intent.
can you please say more about what your use of the photos will be?
in general, private use is ok. the line between private and public has been set at "more than one non-family person" since the days of edison cylinder music. it was ok to play a music cylinder for anyone in your family, and up to one friend, but playing a cylinder for more than one friend, even at a home dance, was adjudged a public perfomance, a publication, where royalties had to be paid.
and now, of course, publication on the web is over that line.
there are some exceptions, e.g. for educational or editorial or artistic or parody uses.
another solution is just to get model releases from anyone identifiable in your photos, or use released models.
--- not forgetting the easy armchair moral legal theory - just use reverse philosophy and put yourself in the position of the public subject you want to photograph.
what would you think, what questions would you have if someone were photographing you as you walked or shopped or drove in public?
