Instructions
Check the feet. The original Barbie has holes aligned with copper tubes in the heels of the feet and the right foot is marked with a "Japan" stamp.
Check the eyes. The original Barbie's eyes look to her right (if you're looking face-to-face with it, the eyes look to your left). The eyes are outlined in black, the irises are white, the eye lids have blue eye shadow and the eyebrows are arched to look like upside-down Vs.
Check the head. The original Barbie had either blonde or brunette hair, so if your Barbie has any other hair color, it's not an original.