@Legatus:
You're right to notice the helmet flash, which was in no way a "standard" uniform item during the Second Afghan War. However, I have a copy of a period photo dated May 22nd, 1879 showing a group of British officers of the 28th Punjab Native Infantry in which two of them wear such flashes on the sides of their helmets, so they were in use with at least one unit, albeit a Punjabi one. Having done a decent amount of research into the uniforms and equipment of the 66th at Maiwand, I would say I doubt its use is accurate for an officer of that regiment, but I would not feel comfortable saying it was not possible.