Call to undefined function imagecreatetruecolor()

My web host recently had me recompile Apache in attempt to fix an issue on my server. Ever since, my thumbnail generation script returns this error:

Fatal error: Call to undefined function imagecreatetruecolor()

Do I need to reactivate/reinstall GD? If so, how do I do this?

httpd.conf is the file you need to edit but because your using CentOS which is a Unix system you will need to run the sudo command as only the windows server comes with GD library pre-installed

The default httpd.conf location on CentOS is /etc/httpd/httpd.conf
Use an editor like vim or nano to adjust the config file as suggested by SgtLegend.

I am not very familiar with Linux or server maintenance. I am running on a CentOS server. Which httpd file would typically be the one I should edit?

In your Apache httpd file find


and simply remove the ; before it. If your on a UNIX system read this