Off stage images being exported/published

1

I have created a nice little animation that requires some off-stage starting points and ending points. My issue is that when I export the .swf the entire range of any image used in the animation is published. I simply want the stage published. An earlier post mentioned a mask that would crop the published data, is this what I need to do? If so is there a tutorial available that would instruct me on how to mask all but the stage?