SMF Mod Site

Mod Name:
Created By:
Spam Prevention
First Created:
January 21, 2014, 11:25:21 PM
Last Modified:
December 31, 2014, 11:04:58 AM
Latest Version:
Compatible With:
Total Downloads:

Download this mod (24kB) [2059]
Manual Install Instructions for SMF

Below are some preview images of what the mod looks like when being used



While the default CAPTCHA used to be capable of warding many automated sign-ups and posts, user experience and reports suggest that it is overly obtrusive in style, making it harder for genuine users to post, which counters the principle behind CAPTCHAs that it should seek to minimise impact on genuine users.

Additionally, the lesser levels of complexity are mostly variations on a theme; randomised angles of letters, random colours and so on - ultimately a modestly advanced bot will be able to defeat it.

This module works by not just providing variations on a theme, but multiple varied distinctive styles of CAPTCHA, which differ compared to the classical styles and as such will likely need bots to become smarter in order to defeat them.

Each style has one or more additions that make it specifically irksome to automate, though no doubt some neural-network based bots will have some headstart on doing so.

It has also recently been noted that audio CAPTCHAs are far from invulnerable from defeat; this module offers the opportunity to disable the audio CAPTCHA for now, pending improvements to SMF's audio CAPTCHA system.


The styles provided by this version of ArantorCaptcha, in alphabetic order by internal module name:

  • 'grid' - draw letters on a grid background
  • 'ledicon' - draw letters as if they are lit bulbs on a board full of LED bulbs (like many automated marquee signs)
  • 'recomposeanim' - have letters build up out of individual pixels randomly
  • 'recomposecycleanim' - have letters build up out of individual pixels, and decompose back to nothing repeatedly
  • 'recomposecycleanim2' - as above, but only to 40%-80% visibility, where a human could read the letters but a bot would have more difficulty
  • 'shadowanim' - have just the shadows of letters build up out of individual pixels, with noise
  • 'silhouette' - letters cut out of 'noise' background, using the effect of negative space to make the CAPTCHA visible
  • 'simpleanim' - simple animation, revealing one letter per frame of animation; each letter appears after a slight delay
  • 'stripes' - criss-crossed stripes, with letters cut out of one of the sets of stripes for the letter to appear out of negative space

Normal behaviour is for CAPTCHA images to be GIF images.


1.0.8 - 22nd January 2014
! Removed 'initial' as it wouldn't work very well on some configurations
! After a long hiatus, updated for SMF 2.0.x including some minor bug fixes
- server long since offline
! This mod is now licensed under the CC0 licence

1.0.7 - 23rd August 2010
! Fixed support in German for non German users, thanks to Dismal Shadow

1.0.6 - 20th August 2010
+ Added support for German thanks to chilly

1.0.5 - 17th August 2010
! Removed ability for ArantorCaptcha to return to SMF's own style (previously a 1% chance of doing so)
+ Extra protection by default against spammers (the AC directory was not protected against people using a known list of files and checking to see what files were available, now it is, at least on Apache due to a sane .htaccess file)
+ Added 'stripes' style as suggested by Asgard
+ Added 'recomposecycleanim2' variation on recomposecycleanim; the changes in logic make it easier to keep separate (also suggested by Asgard)
! Non animated CAPTCHAs default to GIF now so that they don't immediately give away the fact they're different to bots
! Now supports's package server

1.0.4 - 13th August 2010
+ Added ability to disable some types of CAPTCHA
! Modified admin type override check to be more thorough (it is possible, if you are currently logged in as an admin, to force it to display a type of CAPTCHA; this is mostly for my debugging use)
+ More meaningful admin page
+ Added 'recomposecycleanim' style
! Tweaked 'ledicons' style letter R thanks to a suggestion from SleePy
+ Added 'shadowanim' style

1.0.3 - 8th August 2010
+ Added GIF animation class as a foundation
! Version numbers in XML files now only updated when the relevant files change (which is sort of how it was anyway; this is why only package-info.xml refers to 1.0.3)
+ Added 'simpleanim' style
+ Added 'recomposeanim' style

1.0.2 - 6th August 2010
+ Added 'grid' style
+ Added readme
+ Installer now redirects to the visual verification section of the Security/Anti-spam page in admin
+ Added option to disable the audio CAPTCHA
! 'ledicons' blue has changed in colour, orange added

1.0.1 - 26th June 2010
+ Added 'initials' style
! Internal restructure for efficiency and memory reasons

1.0 - 8th June 2010
+ First public release containing 'ledicons' and 'silhouette' styles

This mod is released under the CC0 licence