Centering a JPG called by loadMovie

I have an XML slideshow that runs through pictures of various sizes, some vertical, some horizontal. I want all the images to be centered in the movie, but they all load from the top left corner at the target movie clip’s registration point. Is there any way to get Flash to either 1) automatically get the images’ dimensions during the loadMovie function and center them accordingly, or 2) get Flash to consider the registration point the center of the image, not the top left corner? Preferably without having to manually type each image’s dimensions into the XML file?