The point about zooming in is that, if cock was copied from another picture, the background behind the cock would be a different color. Look on the edges and you can see that the edges are darker, which are leftovers from the trace. It is extremely difficult to get rid of all remnants of the background.
I am no skilled photoshopper but I know the basicss. I have tried, actually. Lighting is a huge problem along with skintone.
I have inspected the picture and I have some thoughts...
1). The penis has aliasing (green pixels) around the entire outline of the penis. Nowhere in the picture is aliasing of that amount and color present.
2). If it is done with photoshop, then they got everything right except for the aliasing (very hard to do, you would have to zoom in and actually delete every little green pixel and most people do not even have the eyes to see what I am talking about, let alone to delete the artifacts required for a seamless cut and paste)
3). There are huge cocks out there and BedheadRed knows what she is talking about (women have been fooled on here before by guys camming with incredibly real looking prosthetic penises) I am not second guessing her, but the green pixel aliasing got my curiosity.
I am not saying that it has been photoshopped, but there is some real plausible evidence that it has been. Plus... he'd have the biggest penis on the planet, giving the late Samson of Cuba a run for his money...
But who knows...