<?php
$img = '';
$thumbnail_width = 100;
$thumbnail_height = 100;
$img_arr = explode(".", $img);
$arr_image_details = getimagesize($updir.$img);
$original_width = $arr_image_details[0];
$original_height = $arr_image_details[1];
if ($original_width > $original_height) {
    $new_width = $thumbnail_width;
    $new_height = round($original_height / ($original_width / $thumbnail_width));
} 
else {
    $new_height = $thumbnail_height;
    $new_width = round($original_width / ($original_height / $thumbnail_height));
}
if ($arr_image_details[2] == 1) {
    $imgt = "ImageJPEG";
    $imgcreatefrom = "ImageCreateFromGIF";
}
if ($arr_image_details[2] == 2) {
    $imgt = "ImageJPEG";
    $imgcreatefrom = "ImageCreateFromJPEG";
}
if ($arr_image_details[2] == 3) {
    $imgt = "ImageJPEG";
    $imgcreatefrom = "ImageCreateFromPNG";
}
if ($imgt) {
    $old_image = $imgcreatefrom("$updir"."$img");
    $new_image = imagecreatetruecolor($new_width, $new_height);
    imagecopyresampled($new_image, $old_image, 0, 0, 0, 0, $new_width, $new_height, $original_width, $original_height);
    $imgt($new_image, $updir.$img_arr[$key]."s.jpg");
}
?>