Changing Captcha Fonts
To change the Image Captcha font you need to open the securimage.php which is inside the securimage folder.

This page is very well commented so that you can see exactly how to change all aspects of the security Image displayed on your feedback form.

To change the TTF (True Type Font). Upload any new .TTF font to the securimage folder and edit the new font name as below. Change the elephant.ttf to your new font name.

Line 170: var $ttf_file = "./elephant.ttf";

Save the securimage.php file and upload it to your securimage folder.

It always pay to make an original backup of all files before editing in case of mistakes.