Jan van Eyck, Arnolfini Double Portrait, signed and dated 1434, London, National Gallery of Art, all rights reserved. Some details of the image:
The bronze chandelier, the signature, the prayer beads and whisk broom, and the extraordinary convex mirror
If you look closely at the above detail, you can see the changes Jan made in the position of Giovanni Arnolfini's hand.
A number of the manuscript images I used in the talk came from the superb website