This program is a wrapper for the 3D reconstruction algorithm of the OpenCV library.
Compile it with (needs libcv-dev, libcvaux-dev and libhighgui-dev):
 $ g++ -O2 -Wall `pkg-config --cflags opencv` `pkg-config --libs opencv` -o opencv-depthmap opencv-depthmap.cpp
Run it with:
 $ ./opencv-depthmap -p 16 -i 2 left.jpg right.jpg

This program is also availabe as a GIMP Plugin:
http://sites.google.com/site/elsamuko/gimp/depthmap
There the depthmap can be used with focus blur to simulate a bigger aperture.

Left image and right image:

(cc) by BdR76

Calculated depthmap (parallax=32, iters=2):