Some people use a jar that's too small and wait until it overflows before taking a picture. After a week, more or less, your starter should double or triple in size before it starts to fall. Choose a jar that will accommodate plenty of rise if your starter is active and strong. Another reason starter may overflow in a jar is the proportion of water to flour. If your starter is too "liquidy," it may grow faster and higher, but it may not be strong enough to support a loaf of bread. High humidity and higher temperatures also make this more likely.