Checkbox in advanced settings of CoronaMtl - check and set material to black.
Photoshop level: unimaginable! 
Awesome news !!! I’ve needed this plenty of times.
Are the shadows it catches from the actual lights in the scene or is it more of an Ambient Occlusion shadow?
it can catch both
Car modelers can not live without it)
Just in time. I’ve been doing a lot more composite work lately, so this will come in extremely handy. Thank you.
Oh, beautiful news! Thanx a lot!
Great! I needed this so much for my work! Thanks!
Perspective is slightly off. or field of view rather…
Very cool Add Man!!!
Great! Thanx a lot!
Yummy! Seems to work
Now we have the ability to do most of the compositing stuff until we have a real matte/shadow functionality.
hmm.. actually, the catcher material does not seem to become completely black.
Great news! Thank you!
beautiful! thanks a lot
I had to hack it 
Why is it only works in Alpha? A beauty - the object is visible
you can use the "visible for reflections/refractions/… to disable the visibility of the material. At the moment I am not sure how to best integrate it into UI
amazing! Thanks!
So it’s not a bug that it’s not completely black… mmhh… strange (not really sure if it’s really useful then).
What exactly is the catcher property “meant” to be used for? I mean, I see it as a quick and dirty way to give people the opportunity to get shadows of their car renderings on a background - but it is not comparable to real matte/shadow stuff.
So what exactly do you want to integrate in a UI?
What happened to this option in the latest dailies?
ohhhh yessss.. great add Ondra