The icon set for an application is displayed when you look for it in the Dash or in the Panel when you are running it. If you find that no icon or a wrong icon is displayed for an application, that can be fixed easily.
There is a
.desktop entry corresponding to every application. It will be either in
/usr/share/applications/. This is just a text file. Open it up and find the
Icon entry. Set it to a path of the icon file, typically a
.xpm file, you want.
Tried with: Ubuntu 14.04