Yes, there is a photo of
James McCudden in leather jacket and flying cap. It appears in Alex Revell's
HITEB (page 309) and also in the 2001 Greenhill reprint of
Flying Fury. The caption states that it was taken in June 1918 when he revisited 56 Sq. However, unfortunately it's quite fuzzy and overexposed.
There are also a couple of photos in HITEB showing JTB in uniform either wearing flying cap or holding it in his hand, but not wearing full flight gear.
The only other flight gear images I have seen are in Alex Revell's 1987 Aces & Aeroplanes bio. This has a couple of pics. of McCudden standing next to a Bristol monoplane and also a close up of him in the cockpit, all wearing flight cap and goggles. Hope this information helps.
Regards,
Brian