What constitutes an ID?

[2Xtreme21]

I'm sitting here looking at the back of my voter registration card and it says "This card is an acceptable form of identification." I'm just wondering how it could work as an ID when there's no picture on it and in general how you are able to prove that you are, indeed, you by presenting something without a picture? What's to stop Joe Schmo from getting ahold of my voter registration card and like, going to Mexico or something?

 

[FoBoT]

voter ID laws vary from state to state

a utility bill is adequate identification to vote in Missouri