packJPG is a compression program specially designed for further compression of JPEG images without causing any further loss. Typically it reduces the file size of a JPEG file by 20%. It is my most well known compression software and possibly the reason why you are here.
Download it from here:
packJPG v2.5k (GPL)
Older versions are available from the Aalen University Homepage.
packJPG has been in development for a long time. It has no known bugs and can be considered stable software. You may be able to crash it if you try very, very hard (won’t happen with any standard JPEG files). If you manage to, a bug report would be greatly appreciated.
packJPG and it’s source code can be used freely under the terms of the LGPL. If that is too strict for you and you only need uncompressing functionality, take a look at unpackJPG. If you want to take up some JPEG development of your own I also highly suggest you take a look at my JPEG Open Source Developers Package.