[Integer] The number of the bitmap corresponds to the glyphs stored in the glyphs folder. Zero means no image is associated with the button. 1 to 39 refer to the default equinox bitmaps that can be added to buttons and 40 onwards will refer to any graphics you add to the glyphs directory. Although the method language refers to the graphics as bitmaps, the properties dialog for the object refers to them as glyphs.

You must save any individual images you want to use on buttons to a directory called Glyphs and select each image from the glyph picker in the properties window of the button. (The Glyphs directory is created when you create a new app, but if you are upgrading from v2/v3 to v4 the directory must be created manually).

Your Equinox client must be stopped and restarted each time you add new images to the Glyphs folder before you can view them.