Add a ‘guide’ image to custom post type admin page

You could add a custom help

Simple example taken from here

function mqw_example_contextual_help( $contextual_help, $screen_id) {

   # Uncomment this to see actual screen
   # echo 'Screen ID = '.$screen_id.'<br />';

    switch( $screen_id ) {
        case 'mycustompostname' : //Your custom post name
            //Just to modify text of first tab
            $contextual_help .= '<p>';
            $contextual_help = __( 'Your text here and the image after.' );
            $contextual_help .= '</p>';
            break;
    }
    return $contextual_help;
}
add_filter('contextual_help', 'mqw_example_contextual_help', 10, 2);