I found it in 'The Frontier Ablaze. The North-West Frontier Rising 1897-98 by Michael Barthorp. Window and Green 1996, ISBN 1859150233
The photo is credited to P.J.Mercer. All I can find in the book is a credit on page 4 to Lieut. Col P.J.Mercer MBE for 'unearthing a fund of useful information ' but it doesn't say where from.