Attached Link: UneekArts

I have never been able to get an answer to this question, that I was comfortable with. Maybe comeone here can guide me or direct me to a good book on the subject. What are the legal issues involving taking pictures of people or things and using them in work for sale. I have an example picture here. Obviously the girls in these pictures could recognixe themselves but in a snapshot such as this, it is near impossible to chase them down and try to get a release form signed. Also, I like to attend and take shots of historical reenactments where people are often dressed in costume. Do I need release forms in a situation such as that? How about objects, such as houses or gates or anything like that? I was recently fussed at by a lady in an open air market because I was taking pictures of items for sale that were sitting on a bench in front of the store. She didn't think "I should be taking pictures of people's product without their permission." Any words of advice on this subject?