Accessibility
A visitor who cannot see or cannot use a mouse cannot drag a slider or click a shape. The badge therefore offers a second path: a non-visual challenge that asks the browser to do the work instead of the person.
How it works
The badge shows an affordance for an accessible challenge. Choosing it sends
accessible=1 with the challenge request, and the server issues the
powonly type: no image, no pointer gesture, just a proof of work computed in the
background. There is nothing to see and nothing to aim at — the visitor waits a moment and
the widget completes.
Because the work is the only cost for that type, its difficulty is fixed higher than the normal band (22 leading zero bits). That is roughly a second or two of a laptop's CPU — comparable to the time a sighted visitor spends dragging a slider, and no audio challenge to transcribe.
The per-site switch
Accessibility is on by default for every site and can be turned off in the dashboard. When it is off:
- the badge hides the affordance, and
- the server refuses
accessible=1for that site anyway.
Both halves matter. Hiding a button is a UI decision; the server-side check is what stops a
bot from setting accessible=1 on a crafted request to get the cheaper path. A site that has
opted out cannot be coerced into it.
Leave it on unless you have a specific reason not to. Turning it off removes the only route through the captcha for some of your visitors.
Privacy
The non-visual path collects no more than the visual one: no cookie, no device fingerprint, no audio recording, no account. It is arithmetic and nothing else.