I can confirm the photo is of a Constable in Inverness Burgh Police, definitely after 1910 (the cap badge was slightly different until then) and before 1930's when the Force adopted the Scottish National ("Semper Vigilo")cap badge.
I am afraid I cannot positively identify the officer (police records do not usually have the shoulder number as that can change over time as officers could be re-numbered to reflect seniority) - I but can at least narrow it down a bit more date-wise.
In 1912 the Force had only 26 (all ranks) and by 1925 it had 32 (all ranks), so we are talking mid-late 1920s for this photo. Inverness Burgh's personnel register, like many forces, was rewritten when a new Chief Constable took over (being a bound volume, it would have a lot of "dead wood" over time, with pages pertaining to officers who had left the force) so the change of Chief provided for a new book to be compiled, containing details only of those officers then serving. Inverness Burgh did NOT have a change of Chief in 1923, but for some reason a new book was started then, with Chief Constable MacNaughton on page 1.
Thankfully that book did not need re-doing for the rest of the force's existence, and latterly the shoulder number WAS recorded against an officer. But "28" is shown as allocated to a Constable who joined on 20th July 1938 (and retired 1964). Chances are he inherited that number from the person who left on the same date as the new man joined, and that man was a RONALD MACASKILL (b. 1886) who retired after 30 years service (as a Constable) on 20/7/1938. Only 2 men left the force in 1938 and the other was an Inspector (who would not wear a number).
That's of course mainly guesswork on my part, but it is definitely a possible.
Does that name by any chance mean anything to you?