VPN doesn't alter your machine or browser footprint just alters your exit node on the web, so it is possible they could still track you with those things. There are a few websites that shoe you how unique or generic your machine, os, screen res, browser etc.
Like if you are an iphone user with safari you are quite generic on the web, if you are using a rare phone, with a modded is, and an uncommon browser you will be narrowed down.