What is this script thingy called?

Hello - I am a shiny new newbie to this forum.

There is a script I am trying to find a tutorial for or any sample .fla’s for. My only problem is I have NO idea what it is called and therefore have had a hard time trying to search for previous threads about it.

To describe it in action: you click on a button and a window where the image will be displayed resizes itself to the proportions of the loading image.

If anyone can tell me the name of this script I would just be forever grateful!