The MkXII had a 4-blade airscrew, the MkXIV a five blade one. I confirm Rene's comment about the carb intake, which is deep and half-round on the MkXIV, and oval on the XII. This is a MkXIVc, as you can see from the wing armament - 2x20mm cannon and 4x.303 Brownings.
Spitfire wingtip types are all interchangeable, so clipped or standard wingtips could be seen on both types. Admittedly, the MkXIIc usually had clipped ones, but so did many MkXIVs.
Finally, RAF Squadrons use cardinal numbers, not ordinal - so it is not 91st Squadron but No.91 Squadron RAF. Just thought you'd like to know.