$ sudo apt-get update
$ sudo apt-get install openttd-opengfx 

openttd-opengfx is installed in your system.

Make ensure the openttd-opengfx package were installed using the commands given below,

$ sudo dpkg-query -l | grep openttd-opengfx *

You will get with openttd-opengfx package name, version, architecture and description in a table

openttd-opengfx package basic information: