resize and replace image using PHP - php

Question

I am trying to resize and replace an image uploaded by the user but the most I can do is resize and output as another file. I have used the library image magician to resize.
If someone can explain how I can do it without using the library it would be better.
public function add() {
$f=Base::instance()->get('FILES');
$fext=pathinfo ($f['usrimg']['name'],PATHINFO_EXTENSION);
$this->copyFrom('POST');
$this->save();
$newName=str_pad($this->_id,5,"0").'.'.$fext;
move_uploaded_file($f['usrimg']['tmp_name'], $newName);
$this->load('id='.$this->_id);
$this->set('photo',$newName);
$this->update();
require_once('php_image_magician.php');
$magicianObj = new imageLib($newName);
$magicianObj->resizeImage(100, 200);
$magicianObj->saveImage('q.jpg', 100);
}

Answer 1

If you want to use gd library, for example you can use this code for resizing jpeg images:
$image=file_get_contents('image.jpg');
$src=imagecreatefromstring($image);
$x=imagesx($src);
$y=imagesy($src);
$y1=100; //new width
$x1=intval($y1*$x/$y); //new height proprtional to new width
$dst=imagecreatetruecolor($x1,$y1);
imagecopyresized($dst,$src,0,0,0,0,$x1,$y1,$x,$y);
header("Content-Type: image/jpeg");
imagejpeg($dst);