Reading the FAQ is a good idea when trying to troubleshoot particular issues. However, it doesn't make the rest of the documentation obsolete - if you can't find an answer here, make sure to have read the entire documentation. Search the support board thoroughly before starting a new support request on the forum.
GD is a graphical library which enables PHP to do image manipulation. The library was originally developped by Thomas Boutell and is now maintained by Pierre-A. Joye under the umbrella of PHP.net. If you are running your own webservem you can download it at libgd.org. You will need to recompile PHP on (L)Unix systems, depending on your setup Apache as well. Most recent versions of PHP come with GD - go for a package. On most windows systems, you can just enable it in the php.ini file. If you are subscribing to a webhost: find out through your webhost if GD/GD2 support is available on your site. If not, ask your webhost if you can have it or find yourself another webhost. GD/GD2 are pretty much a standard feature at most webhosting services.
ImageMagick is another graphical library like GD/GD2 for image manipulation. If you are running your own webserver, you can download it at imagemagick.org. There are sources available for Unix, Linux, Mac and Windows executables, as well as binary packages for various server operating systems. You cannot install ImageMagick if you are subscribing to a webhost.
If you haven't installed Coppermine, yet, create a blank file named "info.php", put this code into it: <?php phpinfo(); ?>. Save the file and upload this file to your webserver, then run it in your browser (e.g. http://www.yourdomain.com/info.php). Look for a table like this:
| GD Support | enabled |
| GD Version | 1.6.2 or higher |
| FreeType Support | enabled |
| FreeType Linkage | with TTF library |
| JPG Support |