//old_contents：待修改的公告内容;
//$content：修改后的公告内容
$oldPic=array();
$nowPic=array();
preg_match_all("/\<IMG(.*?)src=\"(.*?)\">/",$old_contents,$match);
if(!empty($match[2])){
 foreach($match[2] as $key=>$value){
 array_push($oldPic,basename($value));
 }
}
preg_match_all("/\<IMG(.*?)src=\"(.*?)\">/",$content,$testpic);
if(!empty($testpic[2])){
 foreach($testpic[2] as $key=>$value){
 array_push($nowPic,basename($value));
 }
}
$intersectPic=array_intersect($nowPic,$oldPic);//计算交集
foreach($oldPic as $key=>$value){
 if(!in_array($value,$intersectPic)){
 $delPic="图片路径".$value
  unlink($delPic);
 }
}