At a public lecture Einstein offered in Pittsburgh in 1934, at
least four hundred students were there in hall to attend the lecture when
Einstein mathematically derived his well-known mass-energy equivalence
equation, E=mc2. This is believed to be the only remaining photo that displays
Einstein working on that derivation, pulled from a halftone newspaper extract
by David Topper and Dwight Vincent of the University of Winnipeg, who revealed
it in 2007.

If you look thoroughly, you’ll be able see the mass-energy
equivalence in the lower left hand corner of the board on the right. You might find
that the well-known equation states ΔE0=Δm and E0=m as an alternative of the predictable
E=mc2, Topper and Vincent clarify in their paper: "It is the right
blackboard that contains the equation. But its format may disappoint or confuse
the average viewer, because from the start of the lecture Einstein employed the
convention of setting the speed of light c to unity. Hence a close look at the
lower left section of the right blackboard in [the picture] reveals the
relation ΔE0=Δm, and below it is E0=m. As far as we know, [this photo] is the
only extant picture with Einstein and his famous equation."

Source: www.pittsburghmagazine.com