using site_url

I would like to find out how to use site_url or get_site_url instead of using http://mysite.com, can someone please rewrite these following examples so I know how this can be done.

function my_image(){
return 'http://mysite.com/myfolder/image.jpg';
}

function my_favicon(){
	echo '<link rel="shortcut icon" href="http://mysite.com/myfolder/image.ico" />';
}