Search:

You could take a look here

www.programmersheaven.com

Google comes up with a lot of JPEG libraries.

You could try here

http://www.smalleranimals.com/jpegfile.htm

here

http://www.thefreecountry.com/developercity/graphicslibraries.shtml

and there are problably more links.

A very good site to learn the fundamentals of JPEG coding

http://www.ph.tn.tudelft.nl/Courses/FIP/noframes/fip-Contents.html