The anti-SPAM security image is blank.

For the anti-spam image to work, your server must have GD library installed.

You can test if your server supports all the required functions by uploading the gd_test.php file to your server and opening it in your browser.

If you get an error or empty page when opening gd_test.php you should either ask your hosting company to install the GD library for PHP or disable the anti-SPAM image in the HESK admin panel under "Settings".

A complete Hesk anti-spam guide with alternative options is available here:
I am getting SPAM to my help desk