def get_crop_box(width=600, height=1400, center_x=1000, margin_y=15):
    """
    Calculate a cropping rectangle.
    
    Args:
        width (int): The width of the output image.
        height (int): The height of the output image.
        center_x (int): Position along the X-axis for the center of the rectangle.
        margin_y (int): How far down along the Y-axis to position the rectangle.
        
    Returns:
        A cropping box as a 4-tuple, suitable to be passed to Image.crop().
    """
    
    left = center_x - int(width // 2)
    right = center_x + int(width // 2)
    upper = margin_y
    lower = height + margin_y
    
    return (left, upper, right, lower)