The squares are not drawn on a photograph. They are actually painted on the two buildings, road, telephone pole, grass, etc.

Hardesty drew 2 tiny squares on a piece of clear acetate and mounted it in a slide. He took a slide projector outside his house at night and placed it on a table at eye height. He projected the slide across these several surfaces. In the dark, he marked with a grease pencil both sides of each line and where it fell. The next morning, he filled those lines in with spray florescent paint.

From any point of view other than this one, the florescent lines appear to be meaningless random red dashes of different thicknesses. But by standing exactly where the slide projector had been, all the florescent lines join up and appear a uniform width, re-creating the squares. This is a clever reversal of what a painter does, i.e. render 3-D space, two-dimensionally. Here a real 3-D space appears magically flat and vertical.