On the back (v4 on the right)
Different shape of swan neck, different shape of Y incabloc, different color of jewels, overall better finish on gen (i.e. bridges edges polished, teeth on the winding gears polished...), OFFICINE PANERAI engraving is smaller and different font in gen, different color as well.
Minor differences on caseback engravings.
On the front (gen on the right)
Dial
In gen cutouts are sharper, inscriptions more crisp and different font, CP perfectly polished, hands are thicker and better machined. I won't comment on lume color and inscriptions color.
CG (this is a v3 CG)
CG pin with sharper bevel, inner lever has perfect angle, tip has different shape, crown is perfectly machined and polished.
This is what I see, I'm sure there is more.
It's impossible to determine if case is v3 or v4 without pics of the lugs taken from specific angles.