According to Stew, the photographers' details on the reverse of the post card photos are as follows:
1 (left) - SEAMANS STUDIOS,8 KING STREET DOVER 1766
2 (centre) - seems to be foreign and only has CARTE POSTALE
3 (right) - COLES STUDIOS 113 CITY ROAD, B.C AND 90, HIGH STREET, KINGSLAND, N.E.AND AT 82, HIGH STREET, PECKHAM S.E, 192, HIGH STREET, KILBURN, 143, HIGH ROAD, ILFORD, and in pencil 214
They seem to me to be from the First World War, and I believe the cap badge may be from the Grenadier Guards, but I'm sure that the fundis out there will be able to give chapter and verse. You are welcome to post your comments here, by email to me, or to the Derbyshire Mailing List.