how ever if the image is bigger than window size- I want it to maximise the screen
if the image is bigger than the window, the window is by default resized to fit the image, unless the window is already maximized

how do I set a maximum window size to fullscreen maximise(for any screen)
Use showMaximized();

is there another way of hiding label & setting window size smaller until uploading image
explicitly hide the label, use hide(), and add a vertical and horizontal spacers outside the group box