I saw a document on one of the stock sites that explained technical errors with pictures of good images and ones with problems. I can't seem to find where I saw that. I wonder if anyone can point me to a url that explains this?

Thanks
Jamuna

this one?: http://www.istockphoto.com/tutorial_2.1_focus.php

Thanks that helps - but there is yet another one - that shows close ups of accepted and unaccepted areas. Any ideas?

Jamuna

this is the other one i remember reading: http://www.fotolia.com/Member/Training

Dang! That isn't it either...

I found a link on another thread, which is not what I was looking for but has informed me very well. Posting it here for future readers of this thread:

http://www.dpreview.com/learn/?/key=artifacts

Just for funn 
funny photography rules and useful advices:
http://gawno.com/2009/05/78-photography-rules/