$upfile = $_REQUEST['p'];
 
$max_width  = $_REQUEST["w"];
$max_height = $_REQUEST["h"];
 
$def_width  = $_REQUEST["wh"];
$def_height = $_REQUEST["hw"];
 
if(empty($def_width) && empty($def_height)) {
	$def_width = '245';
	$def_height = '245';
}
if ($def_height=='') $def_height = $def_width;
 
//IMAGE PATH
$exportPng = false;
if(!file_exists($_SERVER['DOCUMENT_ROOT'] . $upfile)) $upfile = $_SERVER['DOCUMENT_ROOT'] . $upfile;
else {
	$upfile = "img/nophoto.jpg";
	$exportPng = true;
}
 
//since we already have predefined values of extension
$ext = strtolower(substr($upfile, -3));
 
//INCREASE MEMORY LIMIT WHEN WORKING WITH 
ini_set('memory_limit', '64M');
 
//MAKE NEW IMAGE OUT OF EXTENSION
if ($ext=="gif") { $src = @ImageCreateFromGif($upfile); header("Content-Type: image/gif"); }
if ($ext=="jpg") { $src = @ImageCreateFromJpeg($upfile); header("Content-Type: image/jpeg"); }
if ($ext=="png") { $src = @ImageCreateFromPng($upfile); header("Content-Type: image/png"); }
 
$size = GetImageSize($upfile); 
$width = $size[0];
$height = $size[1];
 
if ($def_width == '') {
	// Proportionally resize the image to the max sizes
	if (($max_width == '')&&($max_height == '')) {
		$max_width = $width;
		$max_height = $height;
	}
	if ($max_width == '')  $max_width  = ($max_height*$width) / $height;
	if ($max_height == '') $max_height = ($max_width*$height) / $width;
	if ($max_height > $max_width)  $highter_dimension=$max_height;
				else $highter_dimension = $max_width;
 
	if ($width == 0) $x_ratio = $max_width;
		  else $x_ratio = $max_width / $width;
	if ($height == 0) $y_ratio = $max_height;
		   else $y_ratio = $max_height / $height;
 
	if( ($width <= $max_width) && ($height <= $max_height) ) {
		$tn_width = $width;
		$tn_height = $height;
	} elseif (($x_ratio * $height) < $max_height) {
		$tn_height = ceil($x_ratio * $height);
		$tn_width = $max_width;
	} else {
		$tn_width = ceil($y_ratio * $width);
		$tn_height = $max_height;
	}
	$dst = ImageCreateTrueColor($tn_width, $tn_height);
	ImageCopyResized($dst, $src, 0, 0, 0, 0, $tn_width, $tn_height, $width, $height);
}
 
if($def_width != '') {
	$highter_dimension = $def_width;
	if ($def_width < $def_height) $highter_dimension = $def_height;
 
	$factor_w = $width / $def_width;
	$factor_h = $height / $def_height;
 
	if ($factor_w > $factor_h) {
		$new_height = floor($def_height * $factor_h);
		$new_width = floor($def_width  * $factor_h);
	} else {
		$new_height = floor($def_height * $factor_w);
		$new_width = floor($def_width  * $factor_w);
	}
 
	$src_x = ceil(($width  - $new_width) / 2);
	$src_y = ceil(($height - $new_height) / 2);
 
	$dst = ImageCreateTrueColor($def_width, $def_height);
	@ImageCopyResized($dst, $src, 0, 0, $src_x, $src_y, $def_width, $def_height, $new_width, $new_height);
}
 
if(!$exportPng)	 Header("Content-type: image/jpeg");
			else Header("Content-type: image/png");
 
 
//OUTPUT INTO PNG TO GET HIGHER QUALITY IMAGE
if(!$exportPng)  ImageJpeg($dst);
			else ImagePng($dst);
 
@ImageDestroy($src);
@ImageDestroy($dst);

http://stuntsnippets.com/php-thumbnail-generator/

<img>

Image thumbnail generator for PHP

php, image

PHP