<?php
 
$img = '<img src="http://w...content-available-to-author-only...t.no/bilde.jpg" width="2000" height="1400" />'; 
 
$doc = new DOMDocument; 
$doc->loadHTML($img); 
 
$node   = $doc->getElementsByTagName("img")->item(0); 
$height = intval($node->getAttribute('height')); 
$width  = intval($node->getAttribute('width')); 
 
if ($width > 1000) { 
    $oldwidth = $width; 
    $width    = 1000; 
    $ratio    = $width / $oldwidth; 
    $height   = $height * $ratio; 
} elseif ($width < 500) { 
    $oldwidth = $width; 
    $width    = 500; 
    $ratio    = $width / $oldwidth; 
    $height   = $height * $ratio; 
} 
 
$node->setAttribute('height', intval($height)); 
$node->setAttribute('width', intval($width)); 
 
$img = $doc->saveHTML($node);
 
echo $img;
 
?>

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