Hello
The information upon the usage of the type V at Escadrille 481 comes from the tradition-air.fr site, wich includes the symbols of all the Escadrilles and some information on each one.
https://www.traditions-air.fr/
If the plane does not belong to the 481 Escadrille, a slight possibility could be that the "V" marking is an individual plane marking. Not really a straightforward information !
Officialy, the Escadrille 481 had 3 "cannon" Voisin VIII and 6 "bomber" Voisin VIII at July 1st 1917 (historical study done by the Marine nationale in 1927). Before, during the three early months of existence, I have no primary source.
For the visual differences between the type III and the type V, they are not obvious. I will check if there one recognizable on a photo.
Regards
Jean