In most Linux distributions now adays there are software centers to help users to install applications, however in order to make applications show a screenshot and long descriptions there is a xml file required[0].
It is recommended that upstream projects create and maintain these files so they may choose which screenshot they wish to display and so on.
0: http://people.freedesktop.org/~hughsient/appdata/
I will leave this to anyone who is interested in this area.