this tutorial is for photoshop
1. open an image, its better if its darker with lots of different colors.
2. go to the top, click select>>select all. then edit>>copy. now, select>>decelect
3. next go to filter>>pixelate>>mosiac a window should pop up like so: 
4. check the preview box so that you can see what it looks like. then scroll the arrow back and forth to change the size of the little boxes. the smaller the cell size, the smaller the squares, and the more detailed it is. it depends on how big your picture is, but for mine i chose 34. you can make it whatever you like, but i think that the best is inbetween 20 and 50. again, it depends on the size of your image. once your done with that, click ok.
5. Now go to layer>>new>>layer, if a window pops up click ok. and then edit>>paste.
6. next go to your layers pallet (if you cant see it go to window>>show layers)
it looks like this:
7. make sure layer 2 is selected (the newist layer that does not have the mosiac effect) and click on the arrow to set the opacity by scrolling the arrow back and forth to whatever you like. i chose 40% for this picture.
8. lastly, go to layer>>flatten image. and there you have it! pretty!
having problems? tutorial didnt work? dont know what something is? Email me and ill see if i can help you!