weird screen pixel problem

I'm new to the forum and I hope I am posting in the right area but recently, about a month or so ago I've gotten really weird problems with my screen. But it will only be on certain things.

For example when I go to youtube (this was only one occasion) the related videos on the sidebar were just weird pixelated boxes that would change, really hard to explain but it just was not a typical sidebar. The other day my background did the same thing. Right now everything is perfectly fine except for when i go to preview some (not all) of the photos on my desktop. It's extremely sporadic and when trying to screenshot the actual problem it won't work so i had to take a photo with my phone.
http://i55.tinypic.com/3518ux2.jpg

I really have no idea what is going on and it just makes no sense, is there anyone who can help?

You didn't tell us anything at all about your machine; year, model, version of OS X, etc.

But generally, if a screenshot does not show pixelation, the problem is not being caused by the graphics chipset. Which means that it may be caused by software or the LCD itself is acting up. Do you have an external monitor or TV? Attach it to your machine and run it for awhile to see if the same thing happens or not.