I have a vague recollection of this, so i can't tell you where to search but i recall an independant little thumbprint scanner that attached to a computer and allowed it to run or only start certain applications associated with that users thumbprint. I wish i could be less vague but my memory isn't what it used to be. I do recall it wasn't so expensive that it was impractical, I just never needed it since i'm the only one who uses my computers.

Maybe search "recognition hardware, software or thumbprint scanner"?