I want to change my main menu background to a custom image, and I've got a few picture in vtf form to use and I've put them in the right place. The problem is that ya_hud (which I'm editing) is set to only ever use the upward background screen but I want it to rotate through 5 images (which is what the default menu does)

Can anyone point me to the file that changes which loading/menu picture shows up?