Create a new symbol by holding down ctrl + F8 or by choosing INSERT>NEW
SYMBOL. Name the first layer on the timeline image. Create a new layer and name
it imageMask.
Import a bitmap photograph in the first layer.
Using the drawing tools create an outline of the object you want to be
cut out on the layer labeled imageMask.
Note: I recommend using Adobe Illustrator 9.0 for doing
complicated vectors. The drawing tools are easier to use and more precise than
most drawing applications. You can place your bitmap into Illustrator and then
trace the image accordingly. Illustrator can then export the image as a .swf
file.
Lastly, right click the layer imageMask and select Mask from the menu.
That's It! You can place this symbol in any timeline of your movie and
animate it however you choose now.