Maybe you can work this into a class as a filler, or as a prompt for a lesson from your syllabus.
Obviously, this came to me over Facebook. I included the FB context because that could be a part of the discussion. You could crop that out if you wanted, but the first picture is already cropped from the full one.
I would show students the first one and get them to talk (or write) about whatever it suggests.
half photo:
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Then show them the full picture, and get them to discuss the illusion
full photo:
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For more interesting photos from Wind Virtual University, http://facebook.com/Shahram.Design
Still more from Vance Stevens 
Actually I tend to use a lot of images in my lessons – either for vocabulary or writing (or any other skill really!). One lesson my students have enjoyed doing is:1 – project an image (the stranger, the better)2 – then in teams they write a collaborative story through EdmodoI then give each team/group the responsibility of proofreading their story and in the end, add a drawing or image to their final product.