Trimage is a useful application with GUI that allows to compress and optimize images using highest compression levels. Currently, Trimage supports only JPG and PNG file formats and gives users the possibility to add images either via the file dialog or simply drag and drop image files directly into the application's main interface.
Installation of Trimage under Ubuntu is very simple, you need to install with this PPA from the command line:
sudo add-apt-repository ppa:kilian/trimage
sudo apt-get update
sudo apt-get install trimage
Search then for Trimage via the Unity Dash (Oneiric & Natty), or start it via the terminal with this command: