[retube]

or you can use a synthetic copy of an eyeball or finger.

for online or remote authentication all bio-metric identifiers are as bad as each other. you can simply "play back" a stolen signiture. if a human is present to observe then maybe it's a little harder. nevertheless, your signiture is effectively worthless if it does get stolen - and when it is you cannot change it.

I'm strongly of the opinion that bio-metric id is a disastrous concept. As well as the issue of having signitures stolen, such systems will evitably result in further erosion of privacy. Plus of course, with possibly the exception of your DNA, you change over time, meaning that, I beleive, such systems can never be that reliable.