I am trying to create a an image of an object (say a cube) and its shadow, with any other pixel except for the object and shadow being transparent, in Blender 2.7. I need this since I will place the resulting images next to several others in Photoshop later, and also as standalones, in a scientific paper which requires that all images have a transparent background.
I know this question has been asked many times before, but all the answers I found are lacking, namely: this question is similar, but the answer uses a "shadow" output of the layer which I couldn't find (I assume it doesn't exist in 2.7?). On the other hand, this video gives a nice solution in case you are trying to place your objects + shadows on top of an existing image by multiplying outputs, but does not produce an image with a transparent background, and I don't see a way to modify it easily.