var
   hHandle: THandle;
   x: integer;
   // visual controls:
   hMenu: TMenuItem;
   Image1: TImage;
...
x:= 10; // десятый пункт меню
hHandle := GetMenuItemID(hMenu.handle, x);
ModifyMenu(hMenu.handle, hHandle, MF_BYCOMMAND or MF_BITMAP,
hHandle, PChar(Image1.picture.bitmap.handle));