Since Guynemer was killed during the war I would say the original photo was taken during WW 1 and not after.
The seller seems to have a whole range of photos of both Guynemer and other heroes including a number of nice car photos. Asking price seems to be in the range of EUR 300 to 500 so if you and I buy the lot we can both declare us bankrupt post payment....
Cheers
Stig