Excluding nobody
The written challenge
A purely graphical captcha makes a registration form unusable for a blind person. That is not a comfort detail: it is a failure, and the module does not expose you to it.
The written alternative is one click away, announced to screen readers, and written in the visitor's language. It draws from three families of prompts:
- an addition spelled out in words — what is seven plus twelve?;
- naming a word by its rank in a list;
- naming a word by its initial, the list being built so that only one answer is possible.
These prompts were chosen so that the answer belongs to a wide space: a counting task whose answer is an integer between one and five is guessed in a few attempts, without understanding anything. Here the answer is a word from the full vocabulary, or a sum among some forty values.