PHP
/**
* image zoom.
*/
function imageZoom($filename,$w,$h) {
/* Arguments meaning */
/* $filename: the source of the name */
/* $w: you want get the image's width */
/* $h: you want get the imgage's height */
$arr = getimagesize($filename);
$src_w = $arr[0];
$src_h = $arr[1];
$src_t = $arr[2];
/*1 = GIF，2 = JPG，3 = PNG，4 = SWF，5 = PSD，6 = BMP，7 = TIFF(intel byte order)，
= TIFF(motorola byte order)，9 = JPC，10 = JP2，11 = JPX，12 = JB2，13 = SWC，
= IFF，15 = WBMP，16 = XBM*/
$src_m = $arr['mime'];

$src_img = imagecreatefromjpeg($filename);

if (($w / $src_w) >($h / $src_h)) {
$bili = $h / $src_h;
} else {
$bili = $w / $src_h;
}
$dst_w = $src_w * $bili;
$dst_h = $src_h * $bili;
$dst_img = imagecreatetruecolor($dst_w,$dst_h);

imagecopyresampled($dst_img,$src_img,$dst_w,$dst_h,$src_w,$src_h);

header("content-type:{$src_m}");

switch ($src_t) {
case 1:
$imgout = "imagegif";
break;
case 2:
$imgout = "imagejpeg";
break;
case 3:
$imgout = "imagepng";
break;
default:
echo "The type was wrong!";
break;
}

$dst_filename = "s_".$filename;
$imgout($dst_img,$dst_filename);

imagedestroy($dst_img);
}
$filename = 'gg.jpg';
imageZoom($filename,100,200);