Well, the message is clear, you're displaying an image (with imshow) and the size of the image is bigger than the size of your screen so it has to be rescaled (to 67% in your case) to fit on screen.
It's only a warning that is indeed not that useful. It always happen if you call imshow with a fixed InitialMagnification or omit InitialMagnification and the image is bigger than your screen. So a simple way to get rid of the warning is to tell imshow to always fit the image to the figure:
imshow(someimage, 'InitialMagnification', 'fit');
Another option is to disable the warning if you don't care about it: