The recommended method of installation is through the software center.
It appears that
the Gimp package was removed from the main repository though. Moved
into the Community-maintained free and open-source
So what you could do if you haven't. Is set the ppa for the (universe) . By left clicking on the top icon in the Unity panel and doing a search for system , then left clicking on the System Settings icon.
This should open a panel with the System Settings icons, left click the Software & Updates icon.
Check the Community-maintained- free and open source software(universe) check box.
Then close it. Go back to the software center, through System settings. Open it and do a search for Gimp. If everything thing went well this will get you the opportunity to install the stable Gimp program for your Operating System through the software center.
Reducing your images for web development is important. You can speed your page load times by doing this. Also your mobile visitors will appreciate this as it reduces the band width. You can add a fast and easy way to do this with a Gimp drop down menu (save for web). Gimp doesn't come with this installed. But the installation is easy through a plug in repository.
If you press the Ctrl Alt and t keys this will open a terminal. Typing
sudo apt-get install gimp-plugin-registry
then entering your password should install the plugins for gimp.
Open Gimp. You will notice that there is a option added to the file drop down list on the top task bar. Save file for web which will compress your image file size for faster load times in a web page.
Disclaimer although you can see that I have done the work on my own system, this does not guaranty that you will not run into issues. Such as dependency issues. By reading this you take full responsibility for any work that you do on your own system (computer). Please join our e-mail list and I will be glad to help you more if you run into issues with this.
Ubuntu and Windows are registered trademarks.
Gimp can be installed from a executable file that can be found at his outside link. http://www.gimp.org/downloads/
The plugins for windows can be found at this out side link. gimp plugins registry
You probably will want the save_for_web_0.28.6_win32.zip
The install is preety straight forward. Left click the Gimp executable first follow the installer instructions. Then follow the same procedure with the plugins.