Oh dear - I'm having trouble bringing this into my reply. It's an eBay item, number:401113454511 and the title is Soldier Group Denbighshire Yeomanry? Welsh Yeomanry at Annual Camp. to be honest, the cap badge doesn't look right to me for the Welsh or Montgomeryshire IY, it looks more rounded at the top, maybe like the Prince of Wales feathers rather than the more angular dragon of the MIY. But I'm on a rapid learning curve and may be wrong.
I'm so sorry I couldn't import the image, but if you do manage to look it up I'd be most grateful.
Aha, groan - I've just noticed that the eBay seller of the postcard has a shop entitled WW1MilitaryPhotographic, so there's a strong clue in there I suppose. DUH! Having said that, even the best people make mistakes, so my query about the image is still worth asking.