PHP implements a method to generate thumbnails of uploaded images by scaling them proportionally to a specified size, _PHP Tutorial

/**
* *
*Constantial scaling
* @param unknown_type $srcImage Source image path
* @param unknown_type $toFile Target image path
* @param unknown_type $maxWidth Maximum width
* @param unknown_type $maxHeight Maximum height
* @param unknown_type $imgQuality image quality
* @return unknown
​*/
function resize($srcImage,$toFile,$maxWidth = 100,$maxHeight = 100,$imgQuality=100)
{

List($width, $height, $type, $attr) = getimagesize($srcImage);
If($width < $maxWidth || $height < $maxHeight) return ;
switch ($type) {
Case 1: $img = imagecreatefromgif($srcImage); break;
Case 2: $img = imagecreatefromjpeg($srcImage); break;
Case 3: $img = imagecreatefrompng($srcImage); break;
}
$scale = min($maxWidth/$width, $maxHeight/$height); //Find the bloom ratio
     
If($scale < 1) {
$newWidth = floor($scale*$width);
$newHeight = floor($scale*$height);
$newImg = imagecreatetruecolor($newWidth, $newHeight);
Imagecopyresampled($newImg, $img, 0, 0, 0, 0, $newWidth, $newHeight, $width, $height);
$newName = "";
$toFile = preg_replace("/(.gif|.jpg|.jpeg|.png)/i","",$toFile);

switch($type) {
case 1: if(imagegif($newImg, "$toFile$newName.gif", $imgQuality))
          return "$newName.gif"; break;
case 2: if(imagejpeg($newImg, "$toFile$newName.jpg", $imgQuality))
           return "$newName.jpg"; break;
case 3: if(imagepng($newImg, "$toFile$newName.png", $imgQuality))
           return "$newName.png"; break;
​​​​Default: if(imagejpeg($newImg, "$toFile$newName.jpg", $imgQuality))
           return "$newName.jpg"; break;
}
Imagedestroy($newImg);
}
Imagedestroy($img);
Return false;
}