Mohamed Magdy wrote:
Is it possible to generate video on the fly containing
random characters
and numbers and use it instead of the still images? or may be generate a
.gif animations (with characters dancing up and down in a colorful way :))?
I assume that can slow ocr (forcing it to convert the video to still
images first then do the ocr) but i don't know about video, may be it is
possible to make the video gives garbage when converted to still
images.. if you google video character recognition you get a lot of hits
but i don't think spammers capable of developing vcr for their needs ;)..
That would most likely make a compatibility nightmare (maybe except for
animated gifs), while not solving any of the before mentioned
acccessibility problems.
I suspect that video captchas in fact can be worse, at least if you
don't consider decoding time, since you give the adversary more
information. If you take all the still images and try to decrypt the
captcha from each of them, you may be able to decode some of the still
pictures, and even interframe information can be used. In a still image
you only have one chance.
On could of cause think of animation that made a word "emerge from the
noise", utilising the human ability to merge a set of still pictures
each too noisy to interpret into an image, but I would suggest to stay
with still images.