This picture has been making the rounds and most sources point to this thread on archerytalk.com.
Sources provided a screen cap of the post, too.
Also provided were the alleged original files:
What's nice about having the original files is that you can examine the EXIF data. Unfortunately, these were not the original files and have both been edited. However, the pixel size of these pictures do not correspond with each other, which suggests manipulation.
So, we're relatively sure that the monster image has been manipulated. The next step is searching for traces of it.
One odd thing I noted is that every leaf and twig seem to be in the exact position in the two photos, as can be seen in this superimposition:
What's odd about that is that, according to the time stamps, these pictures were taken nine days apart. You would expect to see some change. Though, this image proves that the deer photo was not the original photo. The only detectable trace of manipulation I could find is the dark "halo" around the monsters head. Originally I thought that it could have been a shadow, but the IR light cast from the camera originates in the center and this dark area stretches to the left (center). This seems to indicate that the smudge tool was used to blend the foreign object (the monster) into the background image.
None of this evidence supports or denies the claims made that this is a part of a viral marketing campaign of any sort, However it does support the fact that this is a digitally manipulated image.