What is the name of this optical illusion?

It used to be in the NY Daily News on Sundays in the cartoon panel section. There was a hidden picture amidst these colorful blurry dots. In order to see the picture you had to keep the blurred image close to your face and move it away slowly. Then in some weird cross eyed haze you could see an image of something, lol. I know it sounds confusing but I'm determined to find that kind of puzzle again to show my friends who think im crazy.