Can't get the carrara shadow catcher to work properly.
A question of settings or is it not supported?
Shadow catcher
I had a post/thread on this.. just trying to find the link for you..
http://www.Neil-Isted.com
Intel i7 870/2.93 GHz
RAM 16GB
1x Titan (6GB)
2x GTX 660Ti 2GB
Win10 Pro 64-bit
Carrara 8.5 Pro
Carrara - OR4C
OctaneRender™ for Blender
Ds pro
OR Standalone V4
Poser Plugin
Intel i7 870/2.93 GHz
RAM 16GB
1x Titan (6GB)
2x GTX 660Ti 2GB
Win10 Pro 64-bit
Carrara 8.5 Pro
Carrara - OR4C
OctaneRender™ for Blender
Ds pro
OR Standalone V4
Poser Plugin
Sorry, had to remove the link as it was part of the closed testing forum, these images should point you in the right direction though..
If you still need help then just ask
You should then be able to composite your render & background in another program or video editor
If you still need help then just ask

You should then be able to composite your render & background in another program or video editor

http://www.Neil-Isted.com
Intel i7 870/2.93 GHz
RAM 16GB
1x Titan (6GB)
2x GTX 660Ti 2GB
Win10 Pro 64-bit
Carrara 8.5 Pro
Carrara - OR4C
OctaneRender™ for Blender
Ds pro
OR Standalone V4
Poser Plugin
Intel i7 870/2.93 GHz
RAM 16GB
1x Titan (6GB)
2x GTX 660Ti 2GB
Win10 Pro 64-bit
Carrara 8.5 Pro
Carrara - OR4C
OctaneRender™ for Blender
Ds pro
OR Standalone V4
Poser Plugin