CAPTCHA

Completely Automated Public Turing test to tell Computers and Humans Apart

CAPTCHA construction / process:

1. engine_redirector.asp ; Engine_Redirector() redirects /captcha.bmp to captcha.asp
2. captcha.asp interprets the constants Bitmap (size), CodeLength, CharTracking, RndTopMargin, NoiseEffect, NoiseLine, MinLineLength and calls engine_functions.asp PrepareBitmap()
3. engine_functions.asp uses functions PrepareBitmap(), CreateGUID(), RndInterval(), GetCharMap(), WriteCanvas(), DrawLine(), AddNoise(), FormatHex(), SendHex(), SendBitmap()
4. captcha.asp stores the secure Code in Session("CAPTCHA")
5. captcha.asp sends a bmp representing the CAPTCHA image as the response.

The CAPTCHA control has been integrated with the forms engine. The CAPTCHA is not CaseSensive during the evaluation when using forms.

To prompt for a captcha control in the forms engine:

• set your form field type to CAPTCHA
• set the validation rule to CAPTCHA.
• optionally include a default value (not recommended), extended help text, or a custom validation error message.
• The NAME of the form field only needs to be unique, and does not need to be _Code.