How do I create a custom ending image?

[VirtuaroidPilot]

You know that picture of the cake that appears at the end of the game? I want to modify that with a different image. I am working on cleaning up Mradamluigi's Super Rosalina 64 hack (Original mod by TheAnkleDestroyer) and I have made many changes to improve the game experience. I used David's skip end cutscene tweak, and all I have left to do is change the picture of cake to something more relevant to the hack.

Any and all help is appreciated.

Also, I know Kaze released a background editing tool, but I can't find it anywhere and the link he has provided is broken.