Sort pictures by date, newest first in PHP

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PHP

Hi guys, I found a php script online that helps me automatically display images in an image folder, including thumbnails. It works well, but I want to sort my pictures with the newest pictures first in the webpage. Can someone help me do this? Many thanks in advance!

<?php
/* function:  generates thumbnail */
function make_thumb($src,$dest,$desired_width) {
	/* read the source image */
	$source_image = imagecreatefromjpeg($src);
	$width = imagesx($source_image);
	$height = imagesy($source_image);
	/* find the "desired height" of this thumbnail, relative to the desired width  */
	$desired_height = floor($height*($desired_width/$width));
	/* create a new, "virtual" image */
	$virtual_image = imagecreatetruecolor($desired_width,$desired_height);
	/* copy source image at a resized size */
	imagecopyresized($virtual_image,$source_image,0,0,0,0,$desired_width,$desired_height,$width,$height);
	/* create the physical thumbnail image to its destination */
	imagejpeg($virtual_image,$dest);
}

/* function:  returns files from dir */
function get_files($images_dir,$exts = array('jpg')) {
	$files = array();
	if($handle = opendir($images_dir)) {
		while(false !== ($file = readdir($handle))) {
			$extension = strtolower(get_file_extension($file));
			if($extension && in_array($extension,$exts)) {
				$files[] = $file;
			}
		}
		closedir($handle);
	}
	return $files;
}

/* function:  returns a file's extension */
function get_file_extension($file_name) {
	return substr(strrchr($file_name,'.'),1);
}

/** settings **/
$images_dir = 'August/';
$thumbs_dir = 'August Thumbnails/';
$thumbs_width = 200;
$images_per_row = 4;

/** generate photo gallery **/
$image_files = get_files($images_dir);
if(count($image_files)) {
	$index = 0;
	foreach($image_files as $index=>$file) {
		$index++;
		$thumbnail_image = $thumbs_dir.$file;
		if(!file_exists($thumbnail_image)) {
			$extension = get_file_extension($thumbnail_image);
			if($extension) {
				make_thumb($images_dir.$file,$thumbnail_image,$thumbs_width);
			}
		}
		echo '<a href="',$images_dir.$file,'"><img src="',$thumbnail_image,'" /></a>';
		if($index % $images_per_row == 0) { echo '<div class="clear"></div>'; }
	}
	echo '<div class="clear"></div>';
}
else {
	echo '<p>Hang on! I am still growing.</p>';
}

?>

If you have any questions, or need me to clarify something just let me know.


Jerome