There is absolutely no way of determining how big this animal is, given the fact that it is clearly in the foreground and the man is some undetermined distance behind it. However, look at the shadow cast by the animal on the truck bed. It is obviously shorter than the man, and the shadow cast by the chain links appear to be the same size as the links themselves, so there is no reason to think that the shadow of the pig is any different from the actual size of the animal.

Granted, this is one large animal, but just because it was found dining on a dead cow doesn't mean that it killed the cow or is as large as the cow.

The only way you can trust an animal picture to show relative size accurately is if the human figure is as close or closer to the camera than the animal is.