Check out http://null.in:5000
The applications detects if the user clicked on "Submit" or elsewhere.
And this saves user's time of typing weird captcha character.
Just a little proof of concept. This needs a lot of work. Please throw
Having decoy submit buttons is a bit messy.
calculate a value that's added to the posted parameters which verifies
the pointer position was over the submit button when it was clicked?
To get a render-independent but varying value you'd probably have to have
a fixed-size submit button appear at a random position within a fixed-size
area, though a submit button at a fixed relative position to a marker
element would be all that's needed for sites other than those for which
it's worth the spammer's time to independently tune.
1, Wouldn't work with text browsers like Lynx,
2, Wouldn't work if JS was disabled, and
3, Wouldn't work for tab-highlight+enter submits.