I've just installed Plogger on my Debian Sarge box and I'm getting the error message "No GD support detected" when I try to import photos. I have confirmed that my server is running GD2 (ran dpkg --list and found that libgd2-xpm is installed). I've been using another gallery called Minigal which requires GD stuff and that gallery works fine (although it has other non related problems which prevents me from using the gallery). I've had a look through the php code to see how it checks for the existence of GD but can't find any reference to it.
My server details ...
Debian Sarge Linux PHP - 4.3.10 Apache - 1.3.33 MySQL - 4.0.24
It checks by calling a GD function, and exits if the call fails. (This is a guess, but a likely one.) That's why you won't find reference to GD -- it will instead call a function like ImageCreate() (from GD1).
Anyhow, I had the same problem on Windows 2000 Server. The problem ended up being that my configuration script (php.ini) wasn't being read, so even though I had enabled GD in the configuration and had the module installed, it wasn't being loaded by Apache in the first place. But PHP was still loading because it just reverts to defaults, it doesn't error on load. Took me a while to figure this out.
Anyhow, if you have GD installed, run phpinfo(). (Create an empty php document with the function call, and load it in a browser.) If it is configured properly, there should be a section on GD, what image types are supported and what version it is. If not, GD isn't actually installed.
You were quite right. I seem to be having a problem with the php.ini and GD support. There's a entry for GD in the php.ini file but it is not loading it (checked it out in my apache log file). It seems to be having trouble finding it.
I've run up another box with Apache2 and GD support and it seems to be loading correctly so I'm going to upgrade my box to Apache2 and then give Plogger another go.