still image for green screen?

can I use a still graphic image I created in photoshop that has a green background

to create a green screen effect in imovie 11? The file I created in photoshop

is a custom title screen consisting of various type, and a free-form black shape

behind the type- all the rest of the frame has been colored with with a green-screen color. my goal is to have that graphic floating on top of the underlying

video clip while it plays so that the playing clip can be seen behind the type, etc. What file type should the still image be saved as to imported into imovie?

how do I bring it into the project?

thanks for your time!

peter stetler