You know the name of the image if you are opening it -> get it from the filename/path. There isn't a window when you use Open() on image, it will just return the image object (at least doesn't seem to create a window in JMP17/JMP18 when run from script editor).
But you can send << Get Path to that
Names Default To Here(1);
img = Open("$SAMPLE_IMAGES/windmap.png", "png");
//Show(Get Window List() << get window title, img << Get Path);
nw = New Window(img << Get Path,
img
);
And if you have already open windows, Get Window List() << Get Window Title works but you might not know which is your image (last opened window is the last in list).
-Jarmo