The default image driver used by Movable Type is ImageMagick. Sometimes, however, there is a problem with Movable Type and ImageMagick resulting in the following error message in the Movable Type admin area:

Image::Magick is either not present on your server or incorrectly configured. Due to that, you will not be able to use Movable Type's userpics feature. If you wish to use that feature, please install Image::Magick or use an alternative image driver.

The solution is to change the image driver to NetPBM. You can do this by adding the following line to your mt-config.cgi file:

ImageDriver NetPBM

This should resolve the Movable Type image driver issue for good.