The Warping plug-in does geometrical transformations also known as projective mapping or image warping. It uses 4 source and destination controlpoints that are mapped onto eachother, while the whole image is transformed accordingly. It can just as well be used to "undo" warping in an image.
The warping plug-in can be applied to forensic problems such as:

• Synthesizing topviews from (flat) crimescenes.
• Measuring objects in flat scenes with perspective.
• Combining an oblique angle image of a document (to make indented writing visible) with a scan.

The Warping plug-in has been designed for PhotoShop™ compatible plug-in hosts, some of which are free.

Carpark image courtesy Peter Kovesi

Click on the image above to see an example of a topview synthesized with the Warping plug-in, and obtain the plug-in.