I have been playing with merlyn's original code, and caught this (thanks to those helpful monks on CB). I have some ideas around this, which may do one better than PayPal and Yahoo's schemes.
in reply to A little fun with merlyn
Just a few ideas, but then again.. anyone who would try to stuff the ballots on a poll system (versus a login/authentication system) would probably not go to this length... unless that person were jcwren of course.
What if you had an image, an animated .gif file of two layers, where the image "shifted" every 2 seconds by one pixel to the left/right/diagonal?
What about using a transparent .png file, where the pixels that make up the "visible" letters/numbers on the image are actually spread randomly across several layers in the image? Basically like painting on several layers of glass, then stacking them up and looking through them.
How about an image where the entire image was transparent, but the bgcolor of the page, rendered with CSS changed to make the image lettering "visible" in that <div> tag when the user hovered over that section?