automatic resize of images
Fragment of a discussion from Project:Support desk
See $wgUseImageResize or $wgUseImageMagick. Generally this is enabled by default by the installer if you have the needed programs.
Note, in order for re-sizing images to work, you also need to have your webserver have write access to the apropriate parts of the image directory (if uploads work, you probably already do). See Manual:Image Administration
