Image does not show in article and gallery pages

[mondingnibai]

I successfully created a plug-in. I have also a template called show_image, this show image is located below the navbar. I want to show a image right here, so I create a plug-in and call the variable I declare in the show_image. It works, but in the article page and gallery page does not. what would be the problem here?

Here's the plug_in code:

ob_start();

include('image.php');
$my_image = ob_get_contents();
ob_end_clean();

vB_template:: preRegister('show_image', array('my_image' => $my_image ));