Tiny green dots on screen?

I have this issue since a year and never had seen it around on mac forums. So when I play a movie or even grabbing a window around the screen these tiny green-blue dots appear and disappear randomly, sometimes they line up vertically. The smaller is the movie size playing in quicktime (even in youtube) the bigger are the dots. The good thing is I see them while working with pictures in photoshop, but they don't affect the picture quality when I save them in jpg or other formats. The sad thing is when I render movies with imovie or any other video editor: the green dots are sticked and layered on the movie after the export!!!

I have Leopard installed with the latest updates but nothing has solved via software. Guess it is a logic board failure, but any help or suggestion is welcomed!