It's VERY uncomfortable to look at a 3D picture where any part of it seems to be closer than the screen itself.
(eye muscles have to flex to focus on near details, but relax to focus on far details)
To avoid eye-strain, align the L/R pictures so that the closest parts seem to remain in place while the background shifts.


PHOTOSHOP
Create a depth map
Blur the depth map by 5  (at 640x480 size)
Displace original pic by -3...-4 to create left pic  (at 640x480 size)  (Filters > Distort > Displace)
Left = Displaced image
Right = Original image  (shifted so that near objects overlap in both pics)

CREATING DEPTH MAP
Layer setup:
	layer - depth folder
	layer - depth folder  (set to "screen" while editing)
	layer - black at 85% opacity to subdue original picture
	layer - original pic
	layer - black
While shading
	Use "screen" on the current depth folder so that black-shaded farther areas seem to fade into the solid black background
Adjusting overall depth of each layer
	Place a gradient map adjustment layer within each folder
	Each layer is shaded from white to black. The gradient maps adjust the values afterwords to make each depth layer relative to each other overall
Blur the depth map by 5  (at 640x480 size)
	If you don't, then the displacement will duplicate parts of the image at the edges in weird ways.  Blurring completely prevents this.