How can I collect signatures from site visitors?

How would I go about collecting a signature from a site visitor?

I am building my site in PHP and would like to give the user the开发者_如何学JAVA ability to add their signature to a form. They can use their mouse to draw the signature. The signature would be compressed and added to the rest of the form data using the GD library (if possible).

I am open to using Flash, jQuery, or PHP, but I’m not sure where to start.

Please have a look at Capture Signature using HTML5 and iPad. The solution proposed by heycam (with a demo) uses SVG to capture the signature. This svg path is ASCII so it's very easy to manipulate and store without losing precision or quality.