Hasta La Motion!

I’m trying to subtract the RGBA of an image to another and not know how, this is the script I’ve done in Nuke, but the function "minus"from the Merge node does not work as I with, because when you put a background of the same color the teapot stays the persistent color, in the motionblut gradiant.

I have a foreground with a teapot and a background all in the same picture and have the background alone, and want to remove this background from the picture with the teapot and the background together.

Please help, in the attachment is my scene in nuke. Thanks in advance