Including images from Internet

Obviously, including an image from another page can be accomplished with an HTML tag. However, it seems that there are some inherent issues with doing this. How do you keep someone from linking a hi-res image and causing your browser to take forever to return, if you're on a dial-up? Is there someway that PHP can determine the size, via an fopen("http://a.c.com") call or a socket? Or am I totally off base with the need/approach? I'm not looking to pilfer here. I want to allow people to leave a link to their image and then display their picture, as opposed to an icon that links to their picture. Since there may be several different ones on a page, I would expect that you'd have to pre-assemble your page and use PHP to determine size, validity, etc., if that is possible? Is this possible or do the pictures need to exist on the server? Thanks, -- Gaylen