If go to Macau, the baby need the HKID and Return HK permit (this one with photo). Otherwise, just bring along a passport is also OK.
Any photo shop including Fotomax will know the standard of the Immigration Department. In fact, you have better take the picture around the Centre where you are going to apply for the travel documents. Usually those shops knows the standard well. Remember to book in advance so that you do not need to wait.