Core Image and rects

I know this is probably a very basic question, but how do you use the core image library to draw rects and ovals?

coreimage doesn't handle that. NB has built-in rect() and oval() functions. See the tutorial also: NodeBox Primitives. If you need lots of control over shapes, look at the Bezier or http://nodebox.net/code/index.php/Supershape">Supershape docs.