<?php

// This is the temporary file created by PHP
$uploadedfile = $_FILES['uploadfile']['tmp_name'];

// Create an Image from it so we can do the resize
$src = imagecreatefromjpeg($uploadedfile);

// Capture the original size of the uploaded image
list($width,$height)=getimagesize($uploadedfile);

// For our purposes, I have resized the image to be
// 600 pixels wide, and maintain the original aspect
// ratio. This prevents the image from being "stretched"
// or "squashed". If you prefer some max width other than
// 600, simply change the $newwidth variable
$newwidth=600;
$newheight=($height/$width)*600;
$tmp=imagecreatetruecolor($newwidth,$newheight);

// this line actually does the image resizing, copying from the original
// image into the $tmp image
imagecopyresampled($tmp,$src,0,0,0,0,$newwidth,$newheight,$width,$height);

// now write the resized image to disk. I have assumed that you want the
// resized, uploaded image file to reside in the ./images subdirectory.
$filename = "images/". $_FILES['uploadfile']['name'];
imagejpeg($tmp,$filename,100);

imagedestroy($src);
imagedestroy($tmp); // NOTE: PHP will clean up the temp file it created when the request
// has completed.
?>

http://www.4wordsystems.com/php_image_resize.php

How to Resize an Image Using PHP - Image Resizing Script

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