How to retrieve image IDs from shortcode content?

I created a function to retrieve attachment id from it’s src, might work in your case scenario as well

function get_attachment_id_from_src ($image_src) {
    global $wpdb;
    $id = $wpdb->get_var('SELECT ID FROM '.$wpdb->posts.' WHERE guid="'.$image_src.'"');    
    return $id; 
}