Sets the background of a button with a Image

["windflying zhou" <windflying zhou gmail com>]

Hello, everyone
    How can I do this(Sets the background of a button with a Image) please?
In RC file:
    I did this:
style "button"
{
   bg_pixmap[NORMAL] = "1.bmp"
   bg_pixmap[SELECTED] = "2.bmp"
}

widget_class "*GtkButton*" style "button"

But it can't work, then how can I do?
Thank you very much!