Hi Tanya,
As said by
trooper above there is very little insignia (none in fact) to go on and the KD uniform is quite standard. The type of helmet shown was called the 'Foreign Service Helmet' and it was replaced with a different pattern a few years after the 2nd Anglo/Boer War, so I would date the photo to around 1900-02, although it could be a tad later or earlier. It was common for cavalry units to fit their best brass spikes and curb chains to the helmets, as seen in your photo, but that is not to say that some infantry units did not also do so.
As you know from my post at GWF (and
Les above) Subathu, together with Kasauli and Dagshai, were hill depots created by the British Army in the mid-19th c for the families and some of the troops to escape to in the hot weather which was so unhealthy in the plains. They are on the ridges of wooded hills about 20 kms into the Himalayas on the road between Chandigarh and Simla. Kasauli is the major town in the area. It later became the Regimental Centre (or Depot) for the 1st and later also the 4th Gurkha Rifles.
The low-hills village of Subathu was among the first positions to be retained by the British during the course of the Gurkha Wars. This grew to become a fairly large military establishment. It was here that the ‘Nasiri Battalions’, or ‘battalions of friendlies’ from among the Gurkhas were first raised. This is still a recruiting and training centre for Gurkhas in the Indian Army.
Having looked at the postings (i.e. movements) of various regiments I have noticed that those shown as stationed at Peshawur and Umballa (both in Bengal) were often seen in contemporary photos at Subathu. From that I have concluded that these regiments went to that hill station during the hot season. I have gathered that this was something of a vacation in the sense that duties were light and so although the men followed military routine they could also participate in regimental sports and other pleasant activities in the cool climate there. It is also apparent that photographers were not slow to centre their business there in order to get good business both from the soldiers and administrators who also moved there for the so-called "season". It was a time when many parties and balls took place for the families and mothers would try and match make someone suitable for their unmarried daughters and the men would wear their best uniforms in order to look as dashing as possible. There was a kind of class or caste system to this and whereas the officers would tend to marry girls of their class, soldiers would often marry either orphans or the daughters of Anglo/Indians that largely ran the railways and low ranking clerical services throughout India.
If you had a date or some other markings from the photo it might be possible to narrow things down. For example in 1902 the 2nd Battalion of the Welsh Regiment are listed as stationed at Subathu so they are a distinct possibility for your photo.
If you are interested to read further, there is a book about the main hill station, Simla, that can be accessed online here:
http://archive.org/stream/simlapastpres ... 1/mode/2up