import Image

im = Image.open("image.jpg")

if im.size == (7200, 4800):
    out = im.resize((3300,2200), Image.ANTIALIAS)
elif im.size == (4800,7200):
    out = im.resize((2200,3300), Image.ANTIALIAS)

out.show()

dpi = im.info['dpi']  # Warning, throws KeyError if no DPI was set to begin with

# resize, etc.

out.save("out.jpg", dpi=dpi)