how do I check image has loaded or preload images

I have a series of pictures that will be show in a random order. I have a single 'image' on stage and I dynamically change the image by changing the src of the image:

sym.getComposition().getStage().getSymbol("card").$("cardImage").attr( "src", "images/"+cardArray[cardCount]);

However there is sometimes a delay in the new graphic showing, so the old image stays around for a while.

How can I check that an image has loaded, or how can I preload all the images so they will display instantly when required?