php上传图片时生成缩略图

<?php 
function createThumbnail($imageDirectory, $imageName, $thumbDirectory, $thumbWidth, $quality){ 
    $details = getimagesize("$imageDirectory/$imageName") or die('Please only upload images.'); 
    $type = preg_replace('@^.+(?<=/)(.+)$@', '$1', $details['mime']); 
    eval('$srcImg = imagecreatefrom'.$type.'("$imageDirectory/$imageName");'); 
    $thumbHeight = $details[1] * ($thumbWidth / $details[0]); 
    $thumbImg = imagecreatetruecolor($thumbWidth, $thumbHeight); 
    imagecopyresampled($thumbImg, $srcImg, 0, 0, 0, 0, $thumbWidth, $thumbHeight,  
    $details[0], $details[1]); 
    eval('image'.$type.'($thumbImg, "$thumbDirectory/$imageName"'. 
    (($type=='jpeg')?', $quality':'').');'); 
    imagedestroy($srcImg); 
    imagedestroy($thumbImg); 
} 

foreach ($_FILES["pictures"]["error"] as $key => $error) { 
   if ($error == UPLOAD_ERR_OK) { 
       $tmp_name = $_FILES["pictures"]["tmp_name"][$key]; 
       $name = $_FILES["pictures"]["name"][$key]; 
       move_uploaded_file($tmp_name, "data/$name"); 
       createThumbnail("/location/of/main/image", $name, "/location/to/store/thumb", 120, 80); 
       //120 = thumb width  ::  80 = thumb quality (1-100) 
   } 
} 
?>