Provided herein is an apparatus, including a photon emitter configured for sequentially emitting a first set of photons and a second set of photons onto a surface of an article. In addition, a photon detector array is configured to focus the first set of photons scattered from surface features of the article in a first focal plane. The photon detector array is further configured to focus the second set of photons scattered from surface features of the article in a second focal plane, wherein the first set of photons scattered is different from the second set of photons scattered. The photon detector array is further configured to provide information for distinguishing foreign surface features of the article from native surface features of the article.