UV Unproject is a Blender addon for camera resection (camera matching). The script files and a tutorial are available from my webpage.
The current release (0.9.4) is for Blender 2.57. From the user point of view, it is very little changed from the previous version (0.9.3) for Blender 2.49, even though the interface has been completely recoded. The only significant difference is that unprojection is now based on exactly those vertices visible and selected in the UV editor, regardless of whether UV and edit mode selections are synced or not; previously it was based only on UV mode selections, so strange things could happen if syncing was on.
UV Unproject still depends on both NumPy and SciPy, for which Some Assembly Is Required: that’s the price of Blender being an early adopter of Python 3.2.