You don't actually need to use the motion to improve the success rate. Just run the normal algorithm on each frame and elect a winning solution.
Are the people using the captcha-breaking algorithms the ones developing them? Probably not. These things take time... the best way to combat them is probably to change what your captcha looks like and works like every week or so.
As always CAPTCHA is a game of cat and mouse. When something is completely broken, you need to think up something new.