JF Ptak Science Books Quick Post
[The equation in question is at bottom-left; full explanation here.]
I came across an article while researching a work by H.P. Robertson--Lectures on Relativity (Princeton 1935)--and it is much more interesting than what I was actually looking for. It seems that in the history of Einstein working his famous E = mc2 on blackboards around the world that there are no surviving pictures of the man and the chalk and the equation.
In their article "Einstein's 1934 Two-Blackboard Derivation of Energy-Mass Equivalence" (found in the American Journal of Physics, 75 (11), November 2007, pp 978-983) David Topper and Dwight Vincent of the University of Winnipeg sort it out and reproduce a not-sharp (but essential!) halftone newspaper file photo clipping showing Einstein doing just this, using two blackboards for the derivation of the equivalence of mass and energy during a public lecture in Pittsburgh in 1934.
In their short excellent article they do a fine job of discussing the history of these sorts of images as well as provide a nice description of what's ont he blackboard. I urge a reading of the full article found here.