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."