Batch image processing gets easier with the use of BRIC, an operating system independent tool. Its main featueres are currently converting, resizing, rotating and watermarking. Supports over 15 different image types, including PDF. But what sets it apart, from the other tools, is its speed, which are attained by the use of multithreading techniques.
More information about BRIC can be found in the Software Requirements Specification Document prepared by Panagiotis Vasileiadis (click here)
BRIC is free, open source software and it is licensed under GNU General Public License version 3.0 (GPLv3). This specific type of license gives everyone the freedom of owning a copy of the source code free of charge. Also, it gives the permission to share, modify or redistribute the source code which accompanies the software. Furthermore, because the software is licensed free of charge, there is no warranty for it.
http://www.gnu.org/licenses/gpl.html