Sluething an ccurate ID of antique cannons in "period" photos is primarily based on defining characteristics such as:
the presence or absence of a muzzle-swell
bands or rings encircling the barrel
trunnion-shape
cascabel-shape
and (very importantly) the apparent length of the barrel.
In the case of Creskol's very-old photo, due to the lack of a person standing alongside the barrel, its length can only be crudely estimated, by compaing it with the diameter of the wheels. Doing that, I can say it is definitely not a 12-pounder Napoleon cannon ...whose barrel was a bit over 6 feet long. In the photo, the cannon's barrel does not seem to project past the wheels, so it is shorter than a Napoleon.
Going by the presence of a muzzle-swell, and what looks like a 1.5"-to-2"-wide raised band around this cannon's breech end, but no other bands/rings which are large enough to be detectable in the photo... it appears to be a 6-pounder Smoothbore cannon. It could be either a Model-1835, Model-1836, or Model-1841.
And, since I'm sure somebody will ask... no, there's not enough evidence visible in the photo to determine whether it is a yankee or Confederate 6-pounder cannon.