There's a bogus claim that doesn't appear to fit with the facts of the case.
The issues of originality are basically:
(i) specialities of angle of shot, light and shade, exposure and effects achieved with filters, developing techniques and so on; (ii) the creation of the scene to be photographed; (iii) being in the right place at the right time.
Slater didn't set up the shot, the lighting, etc. Slater didn't create the scene to be photographed. And finally Slater wasn't in the right place at the right time: he wasn't actually there at all.
Of course, if he'd set up the shot with a "photo trap" type system, then his absence wouldn't matter, but what even he agrees happened was that he just left the equipment while he wandered off, and the monkey did the rest; critically, he didn't arrange for the monkey to be able to get the camera, he just left the thing alone while he did something else.
Now, had he been smart about this, he'd have ONLY released images that he had post-processed in some way (thereby adding his creativity), but that of course reduces the "authenticity" (and thus the value) of the shot.
The fundamental flaw here is that by promoting the shot as a selfie, he's explicitly admitting that he didn't take the shot. Given he didn't take the shot, it's a desperate stretch to claim that Berne automatically gives him copyright; he wasn't the creator.
Sure, you could argue that he was instrumental in creating the shot, because he set up the camera and collected the results. But under that thinking, you'd have to grant a copyright involvement to the FedEx driver who delivered the camera to you...
Slater doesn’t fulfill every single criterion – but then he doesn’t have to. He has to meet enough. As Tierney explains: