Shortcode for post author photo

Would it be possible to add a custom shortcode that outputs the photo of the post author?

I tried to follow the instructions in this article:
https://support.mailpoet.com/knowledgebase/hook-to-add-your-own-shortcode/

I came up with this code, but it didn’t work. I’m not a developer.

function mailpoet_shortcodes_custom_filter( $tag_value , $user_id) {

    if ($tag_value === 'author_photo') {
        $replacement = get_avatar( get_the_author_meta( 'ID' ), 32 );
    }

}
add_filter('wysija_shortcodes', 'mailpoet_shortcodes_custom_filter',10 ,2);

Is it possible? Thanks.

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