BM_SETIMAGE
wParam = (WPARAM) hBitmap; /* bitmap handle to set */
lParam = 0; /* not used, must be zero */
An application sends the BM_SETIMAGE message to a button control with the BS_IMAGEBUTTON style to set the bitmap handle of the image.
hBitmap
Value of wParam. Specifies the bitmap handle to be set.
This message returns the old bitmap handle used by this image button.
BM_GETIMAGE