BM_GETIMAGE
wParam = 0; /* not used, must be zero */
lParam = 0; /* not used, must be zero */
An application sends the BM_GETIMAGE message to a button control with the the BS_IMAGEBUTTON style to retrieve the bitmap handle of the image.
This message has no parameters.
The return value is the bitmap handle of the image button. If the button this message is sent to does not have the BS_IMAGEBUTTON style, the return value is NULL.
BM_SETIMAGE