mask over images

Hi all,

I was wondering, is it possible in Word to create a "mask" to put over an image? For example, I have a coversheet of a report, and on this coversheet I need a picture to be inserted. But, only on a specific part, shaped like an oval.
I can create an oval shape, and use a picture as fill-effect, but the pucture gets distorted, and I don't want that to happen
I can create a partly transparant image with an external programm, and use that image to be in front of my inserted picture.... Well, that's the way I want it to look, but than I have to use an external program, and I'm not as flexible as I want to be.

Does anybody know how to do this in Word?

Regards,

Bert