Custom visual arrange layers of visualization

Hello, custom visual developers,
does anyone know the command for arranging a background image (PNG), by moving it to the front? I am using a heatmap which I want to arrange it in the background which should appear only parts within an image png file. Currently, the image is in the background but I want to have it actually moved to the front and the heatmap part in the background then the cut-out parts of the PNG image will show the heatmap visualization only there. Which command may I use coding my custom visual in order to arrange the switch between the background image and visual in the front?
Thanks so much!