I've been following Ron de Bruin's examples on creating custom ribbon tabs
but I've ran into a problem. I'm trying to use my own images for the the
buttons but when I replace his image with mine, no image shows in excel

<button id="customButton1" label="Label 1" size="large" onAction="Macro1"
image="largered1" /

I've loaded a bmp image and changed its ID to largered1. I tried the same
thing with a png image, but no success.

What am I missing?