Photoshop :: Compare Two Images And Leave Only Different Pixels?

I'm working together with a photographic studio in order to study better ways to cut subjects in their photos. So, instead of using the ways we use to cut. We have taken 2 photos for the product. The first is only the background, and the second is the beackground with the product. Look at the attachments in this message. It's a simple example (not taken in the studio, with control of lights and so on, but should work for testing purposes).
 
Looking at the 2 images, you can see the bottle and his reflex or shadow is the unique content that changes between the 2 scenarios. If you try, for example, place each file as a layer, group them into a smart object then use stack modes, you can take off the bottle from the scenario. We are trying to find a way to get the inverse (leave only the bottle). So, if finding any combination of technique that works, we could speed time in the cutting process by already taking images this way.
 
(perhaps a combination of blending, use of channels....), anything that could compare the 2 images and calculate the different pixels (this case, the bottle)? or perhaps reach an alpha channel that makes easy to perfectlly cut the image.The difference blending mode, for example, makes a calculation of pixels, but I did not get so much sucess working based on this blend