imagecreatefromjpeg and similar functions are not working in PHP
Install GD Library
Which OS you are using?
http://php.net/manual/en/image.installation.php
Windows http://www.dmxzone.com/go/5001/how-do-i-install-gd-in-windows/
Linux http://www.cyberciti.biz/faq/ubuntu-linux-install-or-add-php-gd-support-to-apache/
In Ubuntu/Mint (Debian based)
$ sudo apt-get install php5-gd