Argyll or Blackwatch?

[Geoff Winnington-Ball (RIP)]

Here's one for you more eclectic types.

My mother was born Margaret MacKenzie Clow in St. Andrews Scotland in 1922, and emigrated here in 1930 with her immediate family. The following picture came to me with her effects after her death in 1983... it is someone in her family (whom I'll never be able to identify), but I can tell you that he has my ears and my son's face. This young officer is photographed in service dress, I'm suspecting circa WW1, but I don't know enough to identify the exact era and regiment. We've looked and looked, and all I can narrow it down to is Argyll & Sutherland Highlanders or Black Watch (I suspect the latter). Can anyone help? I'm sorry the pic isn't better, but it's all I have. I tried this a few years ago, with no luck... maybe this time...

Thanks,

G.