Capture Signature using HTML5 and iPad
Here's another canvas based version with variable width (based on drawing velocity) curves: demo at http://szimek.github.io/signature_pad and code at https://github.com/szimek/signature_pad.
A canvas element with some JavaScript would work great.
In fact, Signature Pad (a jQuery plugin) already has this implemented.
Here is a quickly hacked up version of this using SVG I just did. Works well for me on my iPhone. Also works in a desktop browser using normal mouse events.
Perhaps the best two browser techs for this are Canvas, with Flash as a back up.
We tried VML on IE as backup for Canvas, but it was much slower than Flash. SVG was slower then all the rest.
With jSignature ( http://willowsystems.github.com/jSignature/ ) we used Canvas as primary, with fallback to Flash-based Canvas emulator (FlashCanvas) for IE8 and less. Id' say worked very well for us.