I started playing around with paint on acetate and came up with an image that can be view in two different ways, one with paint and one without... The image is a line drawing in black and white of a building I had drawn the day  before, I then place the acetate over the image and  painted in animal prints on the building, overgrown trees, etc. I thought it was very successful but I would like to develop it more. A number of people suggested layering the acetate, putting a different part of the image on each layer to create the full picture. I think I'll give it a go!