GD 2.0 or later (built in to PHP since version 4.3 or so, but you might need to recompile PHP or contact your host if it's not working).
GD is the graphics library that ZenPhoto is based on. Normally, it should come already compiled in with your PHP executable, but as I found out, it's not always the fact.
Here's how to enable GD2 in PHP:
1) If you have access to your php.ini file...
• Open it up in your favorite text editor and look for the following line (near the middle):
;extension=php_gd2.dll
change it to
extension=php_gd2.dll
(basically, remove the semi-colon in front)
• Save the file and upload it back on the server and overwrite the old file.
• Restart your server
• That's it!
