CAPTCHA with a mask in PHP and JS

Recently I came across an interesting captcha, its difference is that you first need to “wipe” it, and then read and enter it. Example.

I’m interested in the implementation method and maybe there are some examples. Interested in the “mask” itself.


Answer 1, authority 100%

Interesting captcha)

I looked, it turns out something like this:

  1. “Mask” implemented with flash
  2. Flash requests a captcha image at http://l2top.ru/cryptImg.php?key=[key] (the image can only be downloaded once)

It’s quite simple