
Implements a 'CAPTCHA' image.
'CAPTCHA' gotta be one of the worst acronysm i ever came across !
it stands for "Completely Automated Public Turing test to tell Computers and Humans Apart"
Anyway our Captcha here, is the common image with letters/numbers inside which is hard for a computer to parse
but easy for a human.
This is use mostly to prevent "robotized" use of a form to fill your website with junk/spam.