Optical Illusions - a Digital Art Project

I ran across this fabulous art project on Runde's Room early this morning:

I was so inspired by it that I immediately sat down and created a digital tutorial for my Graphic Design kids!  We're doing the Elements of Design next week, and learning the Pen Tool in Photoshop; this was a PERFECT project for both!

Here's my digital version of Jen's project:

And here's the complete Tutorial:

LINE – Creating an Optical Illusion