Edit: Due to the fact that this article is old, the installation instructions may not work anymore. In order to successfully install the latest version of Nomacs, please access the nomacs tag and open the latest article (the one on top).
Nomacs is an open-source image viewer, working on Linux and Mac OS X, under the GNU General Public Licence v3. Nomacs is lightweight and fast and has support for all the popular image formats, like JPEG, PNG, GIF, ICO, BMP and RAW.
The latest version available is Nomacs 3.0.0, coming with changes.
Up to date packages are available via some third party PPA, so installing the software on Ubuntu systems is easy. Add the PPA to your system, update the local repository index and install the nomacs package:
$ sudo add-apt-repository ppa:nomacs/stable
$ sudo apt-get update
$ sudo apt-get install nomacs
Optional, to remove nomacs, do:
$ sudo apt-get remove nomacs
The installation instructions should work on Ubuntu 16.04 Xenial Xerus, Ubuntu 15.10 Wily Werewolf, Ubuntu 14.04 Trusty Tahr, Linux Mint 17.x, Elementary OS 0.3 Freya and other Ubuntu derivative systems.