I'm loving all the vacation pictures that I'm seeing on the forum recently. They are especially welcome in this dreary stretch between winter and full-on spring.

But I've got question that I'd like to get some feedback on that has been bugging me the last few days: Is it OK to take a picture of someone without his/her knowledge and then post it on the Internet without permission?

I realize that I'm much older than many of the forum members and much more concerned about privacy issues than many people these days. I know my students freely post all kinds of pictures and talk about all sorts of subjects on their Facebook pages which are open to the general public. Many seem quite comfortable with that kind of exposure. But I also know, at our university, we are extremely conscious of the need to have written permission before we post any pictures that clearly identify an individual. I'm also wondering how I'd feel if I suddenly saw my image on the Internet, especially if the picture was taken without my knowledge and posted without my permission.

What are the guidelines here? If you are in public place, are you "fair game" if someone takes your picture with an iPhone and posts it without your knowledge or consent. Is posting without someone's knowledge or consent OK if the head is cropped or the person's face is turned away? Is it OK if the intent is to praise, but not OK if the image is used to ridicule or criticize?

What are the "rules" for street photographs? Or are there any rules?