The Captcha (Human Authorization) add-on 1.4.4 now comes with an improved model of generating more difficult-to-guess images (for machines), available to check now on miniBB forums here (on Registration/Anonymous posting), as well as on miniBB.org Demo.

The new option introduced is $innerFontStep, default settings also contain an updated array of $imageColors. The option allows to regulate how neighborhood chars are standing closely, or even "overlapping" each other. While different colors still would allow to recognize rotated and overlapped chars by a human, it sometimes make it harder-to-guess to machines. This feature is already tested live and brought an obvious reduction in automated spam.