What we have here is a way to edit pictures in preview mode. I honestly thought this tutorial was somewhat of a waste of time for me, since I have Photoshop. The essence of the chalkboard effect in this tutorial, is to download chalk fonts (on dafont or some other free type website.)
http://www.wherethesmileshavebeen.com/make-chalkboard-poster-mac-without-using-photoshop/
growingup365 