A "freeview"

Some 3D enthusiasts can view a stereo photograph pair without any special lenses or other devices. This is referred to as "freeviewing." This is a cross-eye freeview. To view this image in 3D, simply cross your eyes until the images merge. It may help to hold your hands on either side of your face, like blinkers on a race horse. Bring them closer together until each hand blocks out one of the images and yet the 3D image is still visible. Don't give yourself a headache, now!