I'm really not a stickler for copyright but I'm curious what the etiquette is when it comes to taking images off, say, google to use on flyers. Obviously, if another band has used the picture already it would be a bit tacky.

But lets say I found a cool but of art on someones site, and by some huge cooincidence he were to see it on a poster for a rock gig, would that be ok? We're a small to medium band in town so I'm not so much worried about the lawyers as looking like we don't know what we're doing.

well i think you could eventually get in trouble, but maybe if you cahnge the picture, add a title maybe change colours or add a frame. also you are allowed to use the picture if you write the source underneath(site from which u took the picture). the source can be written in tiny font so its barely visible, its legal AND the owner of the image will like the extra advertisment but u shud send the site a mail.
hope i cud be helpful!
email dirk gently on the subject, he's UG's legal guy. if anyone can give you a clear concise specific answer its him.
it depends. they might not reserve rights. its possible. but unless they state as such, you have to assume that rights are reserved and that you can't use it. the best thing to do is contact the person.
my name is matt. you can call me that if you like.