More nostalgia. My mum emailed me this photo yesterday.
The chap with the cane is former world light heavyweight boxing champion Georges Carpentier. Mum says "The question is which of the others is related to you and who are the other characters? (I know the answer to the first part only!)".
The filename included the name "Jack" and the message subject was "Racing picture". I wonder how on earth you'd go about finding out about such things. Still it's a nice pic - love the hats and capes!
Update from my mum, after me making a couple of guesses based on bad memory:
Jack is in fact John Cockeram who was a champion jockey - yes the really tiny one! He was in fact my granddad's brother and your granddad's uncle. If anyone can tell you what the uniforms are that would be great. Some important European race meeting probably France or Austria. He did ride for the Aga Khan - and repute has it he married Buster Keaton's sister.