How to check if an image is cached?

I have many buttons that change icons when clicked. Problem is that the first time the icon changes the image is not cached, so there is a couple of seconds where there is no image before it loads.

My plan is to create a bunch of image labels with my images in them, then delete them all once they load. To time it right is there some way to see if an image label's image is cached or loaded? There is a way to check if audio is loaded so why not images?

I did it manually and it cached the images correctly, so I know the concept works.