The bitmap specified in the lptbab parameter can contain multiple images. The number of images in the bitmap must be specified in the nButtons parameter.
The bitmap width should be nButtons multiplied by the image width, and the bitmap height should be equal to the image height.
The default image width is 16 pixels and the default image height is 15 pixels. The default image width and height can be changed using TB_SETBITMAPSIZE. If the size of the bitmap is not the default or if you have multiple images in a bitmap, you must call TB_SETBITMAPSIZE to change the default size settings.