The following link have some very basic briefing in a very odd and different way, some people will find it annoying and some will get benefit. But what ever it is for you, it worth reading, at least for once :)
testingmanual.com
After using lots of image processing tools I find out the most suitable one for application testing purpose. Snagit 9 have pretty awesome features to capture screen shots and modifying it as needed. I find it very very much usefull as a software tester. I think it worth a try. It is a freeware, you people can find it in your preferred download(full) end and also can be found from following links.
Brothersoft
A very simple tutorial for using it can be found in following link and a lot more in Youtube
http://video.techsmith.com/snagit/9/edu/showme/enu/new-user/new-user.asp
