Have some questions to be on the safe side Enable gallery avatars: Yes or No and what is it? Enable remote avatars: Can they link virus? Enable avatar uploading: Can they upload virus is it safe? Avatar storage path: Where can i find avatars that is safe for me to upload to my forum?
Gallery avatars is where you would grab an avatar set and host a set of avatars on your site (a 'gallery'). Various phpbb sites have 'avatar packs' though it's trivial to make your own. Remote avatars - I tend to dislike this as it encourages hotlinking and thus results in broken links. They can't link a virus per se, but someone could do a lot of tracking. Avatar uploading is fine, though it's always important to make sure your server's software remains up to date. They get piped through php which does not let them scale particularly well. phpbbhacks.com has a lot of avatars (I still can't link yet).