It seems likely there are other photographs in some archives which would at least give the location, if not postcards.

It is more than just the length of the necks, though that is a major “tell”. Take the guy on the right, the distance from his clavicle to the top of his head just about equals the distance from his clavicle to his waist line… this is way out of line with normal proportions and cannot be attributed to simply wearing a low-collared shirt. The abnormal proportions are partially because of the length of the neck, but are also because (as someone else noticed and commented on), the head is WAY too big for the rest of the body. Also, look carefully… the heads don’t line up with the centerline of the bodies, they are slightly off center… not really obvious, but enough to make it look funny, which CryptoMaster picked up on. Simply putting a black bar over the eyes would be a little obvious wouldn’t it? The whole point is to make it look like a real photograph, visibly hiding the identities would beg the question… why? Often, the strongest indicator of a hoax are “witnesses” who wish to remain anonymous. In this case, I believe the faces were changed in order to prevent identification of the actual participants, which could eventually lead to the subsequent invalidation of the doctored photo.

I think we are all in agreement that it’s originally some sort of fish/ sea creature which was modified in some way (stitched to a pole and painted… the black pattern running to the tail looks to be painted on, as well as the mouth and eye). The reason I think we are looking at the dorsal area is that, if we are looking at it ventrally or laterally, the gill slits would be showing. You say you don’t see any evidence that we are looking at the dorsal area, so what’s the alternative (aside from it being a total fabrication)? Are you saying that there’s a fish of that morphology that does not have gill slits visible laterally? Rays and skates have gills visible only when viewed ventrally, but their shape rules them out… a mammal would have a blowhole visible on the dorsal side and the tail would be oriented differently. Take the picture and slide it down to the bottom of your screen until the “mouth” is covered up and you are looking only at the upper half of the picture of the creature. All of a sudden it looks a lot like the shape of a large fish when seen dorsally (top down). Looks like they painted a “face” on the top of its head and those markings extending to the tail to make it look like we’re viewing it’s side instead. Possibly a shark with the pectoral fins removed (as Larry suggested), but I think the tendency with a shark that size would be to show us the mouth and teeth… generally a good sized shark makes an exciting enough picture that there’s no need to “dress it up”… because of that, I’m leaning towards some other type of large fish (giant wrasse?).

Similar cards from the same company at the same time had other animal themes. Look at these pictures of people posing with alligators (some of which appear to have been faked).

This Real Photo card shows the Navy hauling in a shark in Nicaragua in about 1912.

I don’t actually buy that the mystery photo is of a real animal. All of the markings look painted to me, especially the face. But, it might be what happened to this poor shark after it was brought to the shore.

that is one weird fish head!

it does look gutted and skinned/peeled/scaled to me.

CryptoMaster is right about the obvious hack job on the faces, I say all three are pasted but only two are somewhat obvious. Why disguise the faces? Maybe to prevent identification (because the actual guys would say it was just a big fish).

But all of this ignores the problem of why is the “fish” sewn to the pole, but it also forgets what this is…it’s a post card! That immediately puts it into the arena of jackalopes and girls in bikinis: