Schooling a Pair in a Brake at Lucas’s Yard, Clerkenwell James Pollard (1792-1867)

The picture has something of this: cavalry, military, man, people, seated, architecture, castle, square, equestrian, guard, soldier, army, traditional, outdoors, sightseeing, war.
Perhaps it’s a painting of a man riding on the back of a white horse next to a man.