"Larry Bud" <la**********@yahoo.com> wrote in message
news:11*********************@g47g2000cwa.googlegro ups.com...
Ok, I don't know what they're called, but you know the form: The page
displays a "code", usually on a similar color background (dark gray),
and the text is all squiggly.
It's an attempt to foil the bots that go out and process forms. The
user has to type in the code they see, when the graphic itself should
be unreadable by character recognition engines.
So, how are the graphics generated, and how do you implement this?
Any links to resources would be appreciated. It's hard to find any
articles when I don't know what to call it!
When I wrote one of these modules a few years back I used ASPImage to create the
graphic - My code created a random number which was then 'fused' (using
ASPImage) onto an existing background image and saving it under a different name
(I used the Session id for the graphic name).
Next the random number is encrypted using SHA256.
The registration form presents the graphic plus an entry field to re-type the
numbers and the encrypted random number is passed in the form via a hidden
field.
On the form processing page the user entered number is encrypted and that string
is evaluated against the value passed via the form. There are other various
checks carried out on the other data entered from the registration form.
YMMV
Lee
