It’s a little strange, since he was a very popular mystery writer in his day, but so far only one other photograph of Philip MacDonald has turned up. (Here’s a link to the earlier inquiry.) This one arrived during this past hiatus, thanks to Juergen Lull in Germany:

      Hi Steve,

   You’ll probably have a better photo of Philip MacDonald by now. Anyway, this one is from the back of a Penguin of 1955 (X v. Rex).

         Regards,

            Juergen