def mono_crop_image(img, crop_pixel):
    """Crop image `img` so as its dimensions become equal (width=height),
    without modifying its smallest dimension
    """
    if img.width > img.height:
        return img.crop((crop_pixel, 0, crop_pixel + img.height, img.height))
    else:
        return img.crop((0, crop_pixel, img.width, crop_pixel + img.width))
