Add screenshot of current page as Open Graph image. Primes the wp.com cache by including the image at the bottom of the page as well.

add_screenshot_as_ogimage.php

<?php

add_action( 'wp_head', 'add_screenshot_as_ogimage' );

function add_screenshot_as_ogimage(){
    
    // default width = 1500 -- 200px minimum, Facebook recommends 1500x1500, max image size of 5mb
    
    echo '<meta property="og:image" content="http://s.wordpress.com/mshots/v1/'.urlencode( $_SERVER["HTTP_HOST"] . $_SERVER["REQUEST_URI"] ).'?w=1500"/>';

    echo '<meta property="og:type" content="website">'."\n";
    echo '<meta property="og:url" content="'. home_url() . $_SERVER["REQUEST_URI"].'"/>'."\n";
    echo '<meta property="og:title" content="'.get_the_title().'"/>'."\n";
    echo '<meta property="og:description" content="'.get_the_excerpt().'"/>'."\n";

}

// Optional
add_action( 'wp_footer', 'add_screenshot_as_ogimage_footer' );

function add_screenshot_as_ogimage_footer(){
    //prime WP.com cache so FB gets the image and not a loading screen
    echo '<img src="http://s.wordpress.com/mshots/v1/'.urlencode( $_SERVER["HTTP_HOST"] . $_SERVER["REQUEST_URI"] ).'?w=1500" width="1" height="1" style="visibility: hidden;">';
}

I've been trying to set the op:image property using the mshots screenshot, although the facebook debugger returns the correct screenshot I'm getting "Composer Data Unavailable: Failed to get composer template data." and doesn't allow the sharing of the post in production. Did you experience any of this when passing mshots screenshot as og:image property?