How to publish a thumbnail image recording

What string to add additional entries to publish a thumbnail image. At the moment I have the following code:

#<KBD>[<?php esc_html( self::get_text_options( 'published-at-text' ) ); ?>]({blogurl})</KBD>

<KBD>[🖥 site →](https://site/)</KBD> <KBD>[📆 site1 →](https://site/)</KBD>

Take a look at the template customization documentation. Adding something like this to your theme’s functions.php file should work.

function my_namespace_publish_format( $input ) {
    Originally published at: {blogurl}<br><br>

    $output = ob_get_clean();

    // Note: the call to apply_filters() that was in the original function has been removed.
    return $output;

add_filter( 'discourse_publish_format_html', 'my_namespace_publish_format' );