Without wishing to underestimate the OP's knowledge of the Army, it is worth saying that the 4th battalion was a Territorial Force unit and so prior to the start of the First World War, he could have been both a part-time soldier and a painter. Obviously once the battalion was mobilized in 1914, he would have been on fulltime military service. Both the 1/4th and 2/4th battalions were sent to India in the autumn of 1914, before then transferring to Basra (1/4th Bn) and Egypt (2/4th) thereafter.
In the photograph he's wearing a good conduct stripe indicating that he had completed at least two year's service with a clean disciplinary record. The fact that he is also wearing a lance corporal stripe indicates a similar minimum length of service, even if he was only holding acting rank.
As Ashtone has said, his medal index card says that he transferred to the Bedfordshire and Hertfordshire Regiment with the regimental number 205795 in the rank of acting corporal. However the card doesn't indicate that he was entitled to the 1914-15 Star which suggests that either he didn't deploy to India with the 4th Hamps in 1914, or that his eligibility for the 14/15 Star was submitted on a separate medal roll and not consolidated on his MIC. If you have access to Ancestry, you can check the Beds & Herts medal roll here:
https://www.ancestry.co.uk/search/collections/5119/ Use his second Regimental number, 205795, as this is unique to him.
Incidentally the Hampshire Regiment did not acquire its Royal prefix until 1946. Prior to WW1, the 4th Battalion was based in Winchester with companies in the following locations:
A Company at Winchester
B Company at Winchester
C Company at Botley (detachments at Chandler's Ford, Bishop's Waltham, Hursley, Mottisfont, Twyford, East Tytherley and Newtown)
D Company at Andover (detachments at Tidworth, Highclere, Burghclere, Kingsclere, Woodhay, Whitchurch and Cholderton)
E Company at Aldershot (detachments at Farnborough, Fleet, Cove and Redfields)
F Company at Yateley (detachments at Crowthorne, Blackwater and Eversley)
G Company at Basingstoke (detachments at Hartley Wintney, Silchester, Odiham and Strathfieldsaye)
H Company at Alton (detachments at Alresford and Selborne)
