Ok, select your geometry you want to add the picture to, normally a plane. And right click on it. Go down to matarials, then go over to assign new material. Then choose lambert. When the attribute editor comes up for the lambert shader, look for a thing called color. You should see a slider, next to the slider there is a checkerboard. Click on that, then choose FILE for the type. Finally, the options for the file shader will come up. Look for a picture of a folder, choose that and then just locate your picture you want to use. Make sure you hit 6 to go into texture view after you have done all this.

Hope that helps, if not just say so.
-RYan