A related aside: while forgeries - deliberate imitations to mislead and deceive - are exciting, they only represent a very tiny portion of art attribution questions. In reality, these tend to deal more with discerning between artists working in the same period, rather than those attempting to fool the eye at several centuries' remove.

For example, the Rembrandt Research Project infamously set out to identify genuine vs. fake Rembrandt paintings in his corpus of known works under the false assumption that there would be a lot of 18th/19th/20th century forgeries. In fact, most of the "non-Rembrandt" cases they found were not later imitations, but instead works done by his own students or contemporaries - or works co-produced by Rembrandt and another. The result - deconstructing the project's original false assumption - proved revolutionary for our understanding of artistic studio practice from the period, but failed to locate many "forgeries" as such.

A review (paywalled, sorry!): http://www.sciencedirect.com/science/article/pii/02604779899...

And a Met exhibition: http://www.metmuseum.org/art/metpublications/Rembrandt_Not_R...