<?php print_post_thumb($post) ?>

// Gets the first uploaded image AND/OR first inserted image into post 
function get_thumb_first_post_image($post,&$thumb_url) {
	//Get images attached to the post   
	$args = array(
  	'post_type' => 'attachment',
   	'post_mime_type' => 'image',
   	'numberposts' => -1,
   	'order' => 'ASC',
   	'post_status' => null,
   	'post_parent' => $post->ID);
	$attachments = get_posts($args);
	if ($attachments) {
   		foreach ($attachments as $attachment) {
       	$thumb_url = wp_get_attachment_thumb_url( $attachment->ID );
                return 1;
		 }
	}
}
// This Prints an image when there is no img in the post 
//Note:you can change the path to your images folder
function get_thumb_no_image($post,&$thumb_url) {
	$content = $post->post_content;
	$thumb_url = get_template_directory_uri() . '/images/thumb_noimage.jpg';
	return 1;
}
// Generates the image with link to the post 
//Note:Change the width and height to your needs
function get_post_thumb($url,$title,$img) {
	return '<a href="' . $url . '" title="' . $title . '"><img src="' .
		$img . '" alt="' . $title . '" width="150px" height="150px" /></a>';
}
// Prints the generated images into theme
function print_post_thumb($post) {
		get_thumb_first_post_image($post,$thumb_url)
	 ||	get_thumb_no_image($post,$thumb_url);
	echo get_post_thumb(get_permalink($post->ID), $post->post_title,
					$thumb_url);
}