Remember putting your two index fingers together a few inches in front of your eyes
and seeing a little sausage between them?
This is similar to that trick, but you cross your eyes instead of letting them relax.
Sit back and cross your eyes so that the double images overlap creating three pictures instead of two.
As the center picture comes into focus it will appear three dimensional.
Tilt your head to the left or right to make sure the images are aligned horizontally. It may help if you try to bring the two images of Mt. Fuji together.
This was created in Photoshop by isolating layers and placing a duplicate set to the right.
Then I shifted elements horizontally on the duplicate set.
Distant elements were shifted to the left and near elements were shifted to the right. I included this information here so if I ever try it again, I will remember how I did it.