Take a look at your admincp
admincp --> maintenance: View Phpinfo
Then look for a section called 'GD' or 'IMAGEMAGIC'. Most likely 'GD' is already installed via your host, some load both.
Code:
gd
GD Support enabled
GD Version bundled (2.0.34 compatible)
FreeType Support enabled
Confirm that this setting is set to GD.
admincp-->setttings-->options-->Image Settings-->Image Processing Library: GD