Question about photos

[Onward]

My question relates to photos I have taken myself.

Let's say I take a picture at an event where they allow cameras or I take a picture of random people on the street. Can I get in trouble if I use those pictures on my websites...does it make any difference if the photos I take are of someone famous?

What about if I take a video myself of someone famous...can I post it on Youtube? or my own website without getting sued? (I know people can sue either way...but I am interested in any legal opinions).

All opinions are appreciated.