Tried to add a header image to the blog.  The image upload function worked fine but after the image was uploaded, WordPress asked to crop the image. Clicking on ‘Crop and Publish’ gives the error:

Image could not be processed. Please go back and try again.

Turns out you need an image manipulation tool called ‘gd’ to make WordPress header crop work. It is a module of php. Installation of gd:

# yum install php-gd

Had to restart apache and now header crop works!