This painting by Linda Clave, LindaClaveArts.com, was used as the cover for The Long Poem. It is available for sale.
What makes this painting so amazing?
When two smaller pictures, an elephant and a red fish were placed opposite sides of the painting, if you looked at the image of the elephant and back again at The Long Poem painting, the image looked 2D (two-dimensional).
And if you looked at the image of the red fish and looked back at The Long Poem painting the image appeared 3D (three-dimensional).