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Environment details? (see Admin panel -> Dashboard -> Information)
You said you are using php 7.2, but the screen shot you made shows PHP 5.6.40.
You haven't told us what OS you are running so telling you how to enable the extension is hard.
On windows you enable it in the php.ini
extension=php_gd2.dll
On Linux you install the php-gd2 package the corresponds with your version of PHP.
