get-images.php

<?php
/**
 * Find all instances of image URL strings within 
 * a text block.
 */
function themeblvd_get_images( $str ) {

	$protocols = array('http://', 'https://');
	$extentions = array('.gif', '.jpeg', '.jpg', '.png');
	$images = array();

	foreach ( $protocols as $protocol ) {
		foreach ( $extentions as $ext ) {
			$pattern = sprintf( '/%s(.*?)%s/', preg_quote( $protocol, '/'), preg_quote( $ext, '/') );
			preg_match_all( $pattern, $str, $img );
			$images = array_merge( $images, $img[0] );
		}
	}

	return $images;
}

// Example Usage:
$str = '
	Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor 
	incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam.

	http://mysite.com/images/test.jpg

	<img src="http://mysite.com/images/test2.png" />

	<a href="https://mysite.com/images/test3.gif">Hello World!</a>
';

$images = themeblvd_get_images( $str );

echo '<pre>'; print_r($images); echo '</pre>';

// Array
// (
//     [0] => http://mysite.com/images/test.jpg
//     [1] => http://mysite.com/images/test2.png
//     [2] => https://mysite.com/images/test3.gif
// )