def construct_image_suffix(img_num, max_len=4):
	"""
		Examples:
			input: (4, 4) => output: '0004'
			input: (10, 4) => output: '0010'  
	"""
	last_suffix = str(img_num)
	img_suffix = ''.join(['0'] * (max_len - len(last_suffix))) + last_suffix
	return img_suffix