I have 2 recommendations, assuming you are referring to lens and perpective distortions:
1. Free, but a bit slow
- Install PhotoFiltre (
http://www.photofiltre.com/), which is a free image editing software.
- Use the native "
Filter>Deform>Trapezoid/Perspective" function to correct for perspective distortions. Since this only corrects for vertical perspective distortion you will have to rotate the picture 90 degrees before correcting for horizontal perspective distortion.
- Install the Fisheye Correction filter created by Raymond FETIVEAU (at the PhotoFiltre website, click on the plugins tab and scroll down) to correct for pincushion or barrel distortion. This filter runs kind of slowly, about 1 to 2 minutes on a 6 MP file (1.8GHz Pentium Centrino notebook PC).
2. Not free, but much cheaper than PS CS2 and faster than the previous solution
-Buy and install Microsoft's Digital Image Standard 2006 (US$26 from
Amazon)
- Download and install Panorama Tools for Windows from
http://www.path.unimelb.edu.au/~dersch/. To do that copy the pano12.dll file onto System32 directory and then copy "correct.8bf" and "perspect.8bf" files into the "plugins" subfolder where Digital Image 2006 is installed.
- Read
this article from dpreview to get the settings for the pincushion and barrel distortion correction filter.