There are two styles of picture button control: picture command button (CTRL_PICTURE_COMMAND_BUTTON) and picture toggle button (CTRL_PICTURE_TOGGLE_BUTTON).
Use SetCtrlVal to set the state of a picture toggle button.
Use GetCtrlVal to obtain the state of a picture toggle button.
Picture command buttons do not have values, so you should not use SetCtrlVal or GetCtrlVal.
Use SetCtrlAttribute with the ATTR_IMAGE_FILE attribute to set the button’s image directly from a file, or you can use SetCtrlBitmap to set the image from a bitmap in memory. Use GetCtrlBitmap to obtain a bitmap copy of the button’s image.