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);