Umui_pagebgimage_bmp

This macro in UMUI sets the background BMP image for a dialog. Is it possible to pass a PNG or JPF image format in the same. Why I asked is because our IT policy does not permit BMP formats.

Probably not if it doesn't work 'as is' by passing it a PNG/JPG.

I'm not sure if/how UMUI works in conjunction with nsDialogs, but there's...

...which does allow you to set JPEG / GIF images on a bitmap control, at least. No PNG support in there.