<?php
 
  $string = '
http://i...content-available-to-author-only...a.gov/image/image_launch_a5.jpg
http://p...content-available-to-author-only...r.fr/programmation/images/mozodojo-original-image.jpg
http://i...content-available-to-author-only...a.gov/image/image_launch_a5.jpg
 
Alot of text
 
http://www.google.com/intl/en_ALL/images/logos/images_logo_lg.gif
 
more text';
 
$urls = array();
$lines = explode(PHP_EOL,$string);
foreach ($lines as $line){
  $line = trim($line);
 
  // ignore empty lines
  if (strlen($line) === 0) continue;
 
  $pUrl = parse_url($line);
 
  // non-valid URLs don't count
  if ($pUrl === false) break;
 
  // also skip URLs that aren't images
  if (stripos($pUrl['path'],'.jpg') !== (strlen($pUrl['path']) - 4)) break;
 
  // anything left is a valid URL and an image
  // also, because a non-url fails and we skip empty lines, the first line
  // that isn't an image will break the loop, thus stopping the capture
  $urls[] = $line;
}
var_dump($urls);
 

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