Display the first image from a post in RSS feed

Question

I have seen another question located here, but it's not useful for my case; it's not working. Also, "RSS Feed Image" plugin is not working as desired.

I want to display the first image of the post in RSS feed.

Below is the code I am using for displaying thumbnail / featured images:

//Display TZ Thumbnail in RSS
function insertThumbnailRSS($content) {
    global $post;
    if ( has_post_thumbnail( $post->ID ) ) {
        $content = '' . get_the_post_thumbnail( $post->ID, 'thumbnail', array( 'alt' => get_the_title(), 'title' => get_the_title(), 'style' => 'float:left;margin: 20px' ) ) . '' . $content;
    }
    return $content;
}
add_filter('the_excerpt_rss', 'insertThumbnailRSS');
add_filter('the_content_feed', 'insertThumbnailRSS');

This one is working sweet, however anything I tried for the first image is not working at all. The least I could do was display the first image URL (not desired).

Answer 1

Here's what I use in Dave's WordPress Live Search to get the first image:

public static function firstImg( $post_content ) {
        $matches = array();
        $output = preg_match_all( '/<img.+src=[\'"]([^\'"]+)[\'"].*>/i', $post_content, $matches );
        if ( isset( $matches[1][0] ) ) {
            $first_img = $matches[1][0];
        }

        if ( empty( $first_img ) ) {
            return '';
        }
        return $first_img;
    }

Answer 2

I used an outside library when I needed to do this. Might be overkill, but I ended up using it again in other areas of my plugin, so it made sense. Feed the post's content to this function, and hook it into those same filters you're using Eventually.

simple_html_dom.php is available here!

function first_image_extractor($description) {
    require_once('simple_html_dom.php');

    $post_html = str_get_html($description);
    $first_img = $post_html->find('img', 0);

    if($first_img !== null)
        return $first_img->src;

    return null;
}