How to set main image without white background?

I see plenty of sellers that set main image without white background even though Amazon has the restriction that suppresses it. It seems like they place the item in a cut-out so that there’s still white around the edges of image. I’ve successfully done it for 2 items, but for other 2 items it seems like it just doesn’t let me for some reason, keeps suppressing it. Is there a way to get away with this consistently?