1. A method to identify whether a candidate object is from an object class, comprising: receiving an image of the candidate object; projecting the received image onto an image subspace, the image subspace being formed from images of known objects of the object class; and determining whether the candidate object is in the object class based on the received image and the image subspace using a likelihood ratio, the likelihood ratio including a first probability density indicating a probability an object is in the object class and a second probability density indicating a probability an object is not in the object class, wherein the first probability density and the second probability density are each a function of a distance of the received image to the image subspace.