use automator to create pop art effect
I think these effects should be built in to iPhoto or Preview, but they don't seem to be. To do this as a work around, follow these steps:
1) Open the Automator Application
2) Choose Photos and Images to start a new workflow. I changed the option to "Ask for photos and images when my workflow runs"
3) In the search field next to variables, type in "Quartz"
4) Choose the "Apply Quartz Composition Filter to Image Files" and drag it to the right (Under where it says ask for photos)
5) Automator will ask whether you want to add a step to copy the image so that you don't save over your original. Choose "Add"
6) In the drop-down menu choose the composition filter "Pop Art" (or whichever you want)
7) Now you're ready to run the workflow. Click the "Run" button, choose the image you want to change, and the new pop art one will be saved on your desktop.