Exporting vBulletin 4.1.7 fails with undefined function imagecreatefromjpeg()
I am working through a command-line export of a large vBulletin 4.1.7 database. The export fails inside core-functions.php, GenerateThumbnail() when attempting to generate thumbnails. The three imagecreatefrom...() functions in lines 120 - 126 are undefined. I can not seem to locate them in the source and was wondering if anyone can point me in the right direction to resolve the function definitions..