Here is our Four Seasons OP Art project. Half of the class did Winter and Spring and the other half did Summer and Fall. From one side you can see Spring on the top and summer on the bottom and on the other side you can see Winter on the top and Fall on the bottom. It's looks better in person:)
Here is how we did it. The students drew their picture on two pieces of paper (I made rular sized lines on them because that part is always hard).
When they were done they glued them onto another piece of paper in a pattern, one strip at a time and then accordian folded it to create the optical illusion.