Second question?

I asked a question earlier. This is kind of similar to that question. I asked, 鈥淎re you allowed to take pictures of strangers without their permission?鈥?br>
My second question is if you do take a picture of someone without them knowing鈥?could you show it in an art show or display it somewhere?

I really don鈥檛 know much about photography.

Yes, so long as you weren't trespassing or peeping. US courts have sided with photographers so long as the subject has no reasonable expectation of privacy.
see this site:
http://www.krages.com/phoright.htm
You do not need a model release if their likeness is not being used in advertisements or other commercial use.

No, if you display it in an art show or publication you have to have a model release from the people in any of the photos.

Only with their approval. They are entitled to privacy.

ahh....not so fast....
1st Amendment

Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the government for a redress of grievances.

If they are the main subject of your photo then I'm pretty sure you need consent but if they aren't the main subject of the photo then maybe so....you'd have to ask a professional....maybe a photography teacher at the local college

My understanding is that, as long as the person is not really recognizeable, you do not need a model release. Otherwise, you do.

Well you need something called a model release form, which is a binding contract between both parties saying you are allowed to use the photo for whatever. If you do not get a release, and the picture is used in print, that person can sue you later down the road. There are many photos taken by famous photographers that have been unseen because the subject did not agree to the model release form...
So to answer your question, yes you can, so long as your show doesnt get blown up and you become famous right off the bat, and that your subjects dont come to the show as well...
-Jason