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I think you've just hit the solution Ada! I like this option because we let the user put the avatar wherever the users wants, from comments to blog posts to snips.
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New approach:

Just like emoticon mechanism , in user's snip he can upload his avatar photo there, and put some code to enable his avatar.

So, combines those 2 actions, maybe we can do:
1. Let user writes some configurations at his owned snip. User can upload his avatar there too.
1. configurations maybe like macro format:
11. \{useSnipSnapAvatar:myavatar.gif\} means show the image "myavatar.gif" for his avatar.
11. \{useGravatar:somebody@somewhere\} means show the avatar from gravatar account.
11. \{useMyBlogLog:url} means show the avatar from mybloglog account.
1. and then, When show some snips, check this snip's owner's config of avatar, and show it or not.

Wow, It sounds a intelligent design....  :p