The photograph shows a group of soldiers at camp somewhere. They appear to be wearing uniforms of WW1 vintage, but there is nothing I can see that is clear enough to indicate what regiment(s) they are and where the camp is. I've enlarged sections of the postcard, which might give a few clues.
1. The shoulder of the soldier on the left has the letters . . . ESTER, but I can't make out any more: Manchester, Leicester, Gloucester? He also has a badge on his arm, but the original is too fuzzy to see clearly what it is.
2. The soldier lying down in the centre has a badge on his arm and also on his cap, but again they are too fuzzy to see anything clearly.
3. The soldier on the right is wearing a slouch hat. Might this be a Yeomanry regiment, and might it even be pre-WW1?
If the photographer came from Leyton (now London E10), presumably the camp was somewhere nearby. I live almost next door in Leytonstone, London E11 and I'm not aware of any WW1 camps in the area. Were camps sited in nearby Epping Forest perhaps?
Any ideas would be most welcome.