Enabling file uploads in MediaWiki
From Tech-Help
Enabling file uploads in MediaWiki requires changing the LocalSettings.php file.
Follow the directions in this section:
## To enable image uploads, make sure the 'images' directory ## is writable, then set this to true: $wgEnableUploads = false; # $wgUseImageMagick = true; # $wgImageMagickConvertCommand = "/usr/bin/convert";
If you have installed ImageMagick on your server, delete the # signs that comment out the last two lines. Otherwise MediaWiki will not be able to make thumbnails or resize images.

