A bit late, but I was researching random numbers and Jono Moore put forward a function for the Universally Unique Identifier (UUID).
You could set up two textfields: captcha and userInput
the calculate event of captcha would have the following Formcalc:
var vUUID = Uuid(1)
$ = Left(vUUID, 😎 // returns a random alphanumeric 8-digit code
if (this.rawValue = captcha.rawValue)
submitButton.presence = "visible";
submitButton.presence = "hidden";
The submitButton presence should be initially set up as invisible/hidden and you can shorten the code to less than 8-digits.
Hope that helps,
chars = "abcdefghkmnpqrstuvwxyABCDEFGHJKLMNPQRSTUVWXYZ23456789";
var sCaptcha = "";
i = Math.floor(Math.random() * 53);
sCaptcha += chars.charAt(i);
this.rawValue = sCaptcha
This way you can avoid having similar characters in the field (i, I, l, 0, O). Use a clear font and large font size.