There is an argument against doing that, actually. Some users aren't going to want you to change your window based on their screen size or resolution- in theory, they have it set up that way because that's how they want it, and it sort-of goes against Java's ideals (in my humble opinion, anyway) to work around them. If a user wants your window to be bigger, the user can either change the screen resolution or the frame size.
It might even be impossible to fully work around- you can get the screen's resolution, but not its physical size. And without that, you can't know how big your frame actually is.
That being said, what you could do is look at how your images are being downscaled. Or you could just allow the user to resize the JFrame at will- you might have to do something to keep the proper aspect ratio (or not), but it will give the user the most freedom.