I am unclear what changed to cause the issue, but one of my zenphoto sites stopped displaying graphics. I thought I would upgrade to see if it would fix it, and got the error that there was no PHP GD. However, that extension is still enabled, and I didn't change that. I have another site on the same server with the same PHP version that works just fine. What can I check to try to figure out what is missing? I did make some settings adjustments at the php version level for the latest PHP vulnerability issues, but this should have impacted both sites if it was that.
GD is a so called bundled extension that normally is included in a standard PHP setup but not required. Technically it could get lost on a PHP update (which is host domain unless you do that yourself). Your error normally appears if it isn't there for some reason.
Please check the following:
I'm on a VPS using WHM. Neither GD nor Imagick are enabled in PHP info. Check box is there but error says Imagick extension is not available. However, in EasyApache4 pecl-imagick is enabled for the php version I am using on the server as well as gd extension. Command line confirms gd is there. As mentioned, another site I have uses the same php install and works just fine, so maybe it is some issue with my install? This isn't php version specific because the same issue was present after upgrading. Pretty strange.
Also, I'm assuming this gd error issue would cause zenphoto to retain the setup prompts, since I can't get them to go away.
I'm almost tempted to do a fresh install instead of an upgrade but that's a lot of work also...
If neither GD nor Imagick are listed on phpinfo they are not (properly) there. Therefore ZP cannot detect any.
I can only guess that same PHP version on your server does not mean same PHP installation thus they differ. Check the php.ini if any extension perhaps is commented out (not loaded) for some reason. Sorry, otherwise I can't help any further as I don't setup my own servers.