2 questions about AVATARS (vB 4.2.1)

[Mephistoxz]

1)
Ok, first of all, I want to know why wouldn't be a good idea to render "external avatars" instead of storing them directly into my DB, so I get rid of that link "image.php?u=10912&dateline=1386613040"?
I know about the image's uptime, I don't worry about broken links of avatars' URL

I mean, if I want to show avatars like this:

<a class="postuseravatar" href="member.php/10912" title="MEMBERS is offline">
				<img src="http://i.imgur.com/h12js5.jpg" alt="MEMBER's avatar" title="MEMBER's avatar">
			</a>

instead of this

<a class="postuseravatar" href="member.php/10912" title="MEMBERS is offline">
				<img href="member.php/10912" alt="MEMBER's avatar" title="MEMBER's avatar">
			</a>

HOW TO DO THAT?

2)
I've installed a new template, and I need to modify the allowed size for avatars to a new smaller size.
I can't resize each user avatar, so I want to RESET them.
How can I reset all member's avatars so they have to upload a new one with the new dimension rules?

Thanks in advance!