<?php
$pat = "!src=\"([^(\"|http)]*)\"!ieU";
$str = 'src="http://www" ';

if(preg_match($pat,$str)){
    echo "匹配成功";
}else{
    echo "失败";
}

$pat='/(src\=[\"\']?http)+|(href\=[\"\']?http)+/';
$str = 'src="http://www" ';

if(preg_match($pat,$str)){
    echo "匹配成功";
}else{
    echo "失败";
}

------解决方案--------------------
方括号中的内容是一个个并列的字符，不是你这样成组使用的

你可能需要的是这样
PHP code
$pat = '/src="(?!http).*"/iU';
$str = 'src="http://www" src="ftp://www"';
echo preg_replace($pat, 'xxx', $str);

------解决方案--------------------

像这样？非http:,http://www.开头的，补全URL？

PHP code
$testurls = array(
    'http://www.freenewspos.com/italia/creativecommons-photo-album#!POS__calcio&num=0',
    'freenewspos.com/italia/creativecommons-photo-album#!POS__NBA&num=0',
    'www.freenewspos.com/italia/creativecommons-photo-album#!POS__Twilight&num=0'); 
foreach($testurls as $singleurl){
    echo preg_replace('#(?:http(s)?://)?(?:www\.)?(.+)#', 'http\1://www.\2', $singleurl).'<br />';
}