Funny PHP-based captcha for less frequently used forms:

Randomly generates an arithmetical problem (addition and subtraction in the value range of 1 to 25) and then processes this Task to a verbalised word problem (in German, but can be adapted easily - scr ipt documentation in English).



As the captcha-task needs some user effort in terms of workload because the user needs to read the word problem this captcha should only be used for forms that are not often accessed by one single user (e.g. registration forms) as this might produce frustration.