ffdn.org/sites/all/modules/captcha/image_captcha/fonts

It possible to put your own fonts for the Image CAPTCHA in this folder.
However, this is not the recommended way, as they can get lost easily during
a module update. The recommended way to provide your own fonts is putting them
in the files directory of your Drupal setup or, just like with contributed
modules and themes, in the "libraries" folders sites/all/libraries/fonts
or sites//libraries/fonts.