Ok, first a disclaimer. I can hardly spell 'PHP', let alone advise anyone how to do anything with it. But...
I had exactly the same error message dealing with a CAPTCHA just yesterday and, in the end, despite phpinfo saying all was well with gd2 I had to edit my php.ini file by uncommenting the extension=php_gd2.dll line, and ensuring that the path to the loadable extensions was correct. A quick reboot after that and all worked just fine.
But there's still error with "["JPG Support"]=> bool(false)". Now i can use imagecreate becase gd built, but i cant use ImageCreateFromJpeg becase JPG Support not enabled.
I've searched on the web, and i found that libjpeg library must be installed and php must built with "--with-jpeg-dir[=jpg_lib_dir]" configure parameter. I installed libjpeg library, but php can't find libjpeg.so or libjpeg.a
And i found the problem at last :)
I build libjpeg with ./configure --enable-shared --enable-static
Now php can see libjpeg files, and everything is ok.
Maybe this solution will be help someone another day.