This frame contains an "anamorphic" picture - to see the distorted image correctly you need to place a cylindrical mirror on it. The original image can be seen in the reflection. These pictures were popular in Victorian times.
To make your own anamorphic pictures you need a cylindrical mirror, which you can buy or make out of mirrored card or plastic. Some books of anamorphic pictures come with a mirror and these work very well. They also provide some great examples to inspire students.
Draw a circle around the base of the cylindrical mirror. Draw a number of concentric circles outside this one and equidistant from one another. Now draw lines across the diameter of these circles, dividing the circles into equal segments. This is your circular grid.
You now need to create a rectangular grid of equidistant lines, making sure that the width of the grid is less than the number of squares around the circular grid.
Now create an image to make into an anamorphic image. Draw this on to the rectangular grid. Keep it simple, as complicated images are difficult to translate and don't always give pleasing results.
Copy each square of the rectangular grid on to the circular grid, leaving the space around the inner circle clear.
Now rub out all the grid lines, leaving only the image and the central circle. Place the mirror in the central circle. You should see your original image recreated in the mirror.
Sophie Duncan is project manager for science at the BBC www.bbc.co.ukscience