Always get permission
I got a very cross email yesterday from a photographer. We used one of his images in our Pete Tong on Podcasting feature without permission.
It was a mistake. The licence of the picture didn’t state you needed permission (it said it’s OK as long as you credit the photographer which we did by linking to his flickr page).
Clearly I had broken the unwritten etiquette rules around photo permissions. Which I did apologise for, and we have resolved the issue.
If you want to use images properly online I recommend this page on free stock images. Don't learn the hard way like me.
What have I learned? Always get permission!