Sorry Clint can't make that serial out ( but looks like 3 digits); neither of the other 2 seem to have been recorded.
Kempf's D.III had this distinctive wide white bar ; there is another photo of these 2 in the Osprey Albatros aces part 1, with Bassenge's. Another photo of this D.III running-up with Kempf in the cockpit shows the dark fuselage and wheel covers.
The painting is by Brian Knight GAvA.
http://www.vintageaviation.net/kempf5.htm
Nick