Photographs of soldiers in Salonika for sale on eBay are not unusual, but to have one with the full name and date of the photo is.
As an added bonus, the seller has done some research on Private Monkman:
M2/193182 Pte Harold Monkman attested on 7.6.1916. He gave his occupation as a Driver for [ Architect & Surveyor ]. His home address was given as 33 Huntingdon Rd, York. He had previous service with the West Riding ASC. His next of Kin was given as his Brother: Wilfred Monkman of 215 Warwick Rd, Carlisle. He was posted to the Grove Park Reserve Depot on 7.7.1916 and posted to Salonica 10.8.1916. His unit is not visible on the papers though the Unit was serving with the 27th Division. In 1919 an application for a pension states that he has been suffering from Malaria.