How to check if GD Library is installed?

I have a dedicated server and under root i went to Software – Apache Update and on the list i saw GD (version 2.0.15) i am assuming thats GD Library. i checked that and started the build. After everything was done i go back and GD is still unchecked!
Did it install? how do i check if it is installed? how do i install it if i did it wrong?

See original post by netpox