Install or add ImageMagick on CentOS 7 from command line
Craft CMS suggests installing ImageMagick on your server but you can probably get away without as long as you aren't uploadng animated GIFS. If you are, and you're running CentOS 7 with cPanel WHM then the following worked for me recently
yum install gcc php-devel php-pear
// This just said no packages available so nothing to do.
yum install ImageMagick ImageMagick-devel
// this installed it on the server but not as a PHP extension
Then, within WHM: Software > Module Installers > PHP Pecl (manage), search for "imagick" and click install.