“There has been an error cropping your image.” solution

I encountered this “There has been an error cropping your image.” error in WordPress when I tried to crop an image for theme header.

The solution is surprisingly easy.

sudo apt-get install php5-gd

This will install the PHP GD library for image processing.

Update: You may need to restart apache server for it to come into effect.

Source: https://wordpress.org/support/topic/image-issues-cropping#post-6230879