Jpegoptim can optimize / compress jpeg files. Jpegoptim support lossless optimization, which is based on optimizing the Huffman tables. So called, "lossy" optimization (
compression) is done by re-encoding the image using user specified image quality factor.
Jpegoptim Installation:Open up the terminal and type following command to install Jpegoptim:
sudo apt-get install jpegoptim
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source:http://linuxpoison.blogspot.com/2011/01/135781677511822.html