There is a small, low-quality photo on the dedication page of Partial differential equations, by Lipman Bers, Fritz John and Martin Schechter, New York: Interscience, 1964.
If one has a good use for a clearer photo, one might hope to contact his mathematical descendants or his son, R. James Milgram, a professor emeritus who has been active at his Stanford Math email address during the past year.