How can I draw freehand circles on screenshots? In Windows I can happily fire up MS Paint and draw freehand circles with the brush tool on top of my screenshots.

In OS X if I open up a screenshot with Preview and use the pen-looking thing and draw a freehand circle, it's automatically converted into a soulless oval. I also can't draw squiggly arrows or poorly scrawled text.

Short of launching Photoshop (or whatever non-default app), is there a baked-in way to draw freehand circles in OS X?
But you can draw freehand circles in Preview, just select the shape you want to use in the upper left corner after you draw the shape. If you don't see the controls as below, go to View &rarr; Show Markup Toolbar