This is pretty nifty. I grew up in the woods, so I was able to instantly pick out the poison ivy from the not-poison-ivy in all of these without any trouble. But not everyone has my advantages, and I know a lot of people have trouble with this. This site seems like a good way to build your poison-ivy pattern recognition skills.
Source: Poison Ivy Quiz | The Poison Ivy, Poison Oak, Poison Sumac Site