Default Featured Image from Post content

Ok guys.. I got it finally working with my below code.

function wpse55748_filter_post_thumbnail_html( $html ) {

    // If there is no post thumbnail,
    // Return a default image
    global $post;
    $pID = $post->ID;
    $thumb = 'large';
    $imgsrc = FALSE;
    if (has_post_thumbnail()) {
        $imgsrc = wp_get_attachment_image_src(get_post_thumbnail_id($pID),$thumb);
        $imgsrc = $imgsrc[0];
    } elseif ($postimages = get_children("post_parent=$pID&post_type=attachment&post_mime_type=image&numberposts=0")) {
        foreach($postimages as $postimage) {
            $imgsrc = wp_get_attachment_image_src($postimage->ID, $thumb);
            $imgsrc = $imgsrc[0];
        }
    } elseif (preg_match('/<img [^>]*src=["|\']([^"|\']+)/i', get_the_content(), $match) != FALSE) {
        $imgsrc = $match[1];
    }
    if($imgsrc) {
        $imgsrc="https://wordpress.stackexchange.com/questions/283546/<img src="".$imgsrc.'" alt="'.get_the_title().'" class="summary-image" />';
        $html = $imgsrc;
    }

    if ( '' == $html ) {
        return "https://wordpress.stackexchange.com/questions/283546/<img src="' . get_template_directory_uri() . '/images/default-featured-image.png" />';
    }
    // Else, return the post thumbnail
    return $html;
}
add_filter( 'post_thumbnail_html', 'wpse55748_filter_post_thumbnail_html' );

Here I first search the post content with regex if the content have any kind if