Tool for high picture compression with low loss of quality

If you want an easy to use tool, try Trimage, which can be found in the Software-Center of Ubuntu. I've also tested pngcrush and optipng but I have to say that Trimage had the best compression rate of these three tools, without having to mess around with the console :-)

sudo apt-get install trimage

I know pngcrush and optipng.

There is also pngquant and pngnq but those are lossy when the original was in truecolor.

For photos you probably want to convert to JPEG instead.

You should take a look into the new WebP format and the tool provided by Google. Is not very useful right now, but according to Google it has 40% size reduction over jpeg, without additional quality loss.

http://code.google.com/speed/webp/

http://en.wikipedia.org/wiki/WebP

http://ubuntuforums.org/showthread.php?t=1585577