Not sure if it is default on already (I never noticed an issue with that before)... However, you can set it up so that when a new user joins they can turn avatars on during the sign up process.
Go to the control panel under Registrations... go to registration screen. Go down to the avatar function and select Show or Show and Require. If you select show... it will show the option but not require an answer. If you select show and require, they will be required to respond if they want avatars on or off. This is useful for people with slower connections to have a choice if they want to wait for avatars to load when they select a forum to read or not.
Dunny
