Declan McCullagh <declan@well.com> wrote:
I had thoughts along a similar line as Peter's, except to use numbers. Include with <img> tags some .GIFs and ask the person/bot to type in the numbers in the GIFs. Generate the filenames randomly and expire them after five minutes. Should take you 10 minutes to write a prototype CGI script in Perl.
This is done somewhere already. I can't quite remember where, but I suspect that it's in the EBay registration process. "For security purposes, retype the numbers to the left." The numbers aren't vertically aligned, have erratic horizontal spacing, and are presented against a grid-pattern background. I'm not sure if this actually helps much against standard OCR, although I'm pretty sure that the SVMs I work with could be easily trained to translate the GIFs to text. -- Riad Wahby rsw@mit.edu MIT VI-2/A 2002