How do I knockout the backgroud on jpeg image so another backgroung image is visible?

Support Materials and Textures
1

I want to knockout the plain background on an image of a sax player in the foreground so that a nice cloudscape can be seen moving behind him. How do I knockout the background on a jpeg image so another background image is visible? I’m new to Blender and need help.

2

take an image editor and remove the unwanted part to make it white
then this can be made to be invisible or with alpha = 0!

happy 2.6