Drupal provides same header for the whole site and if we want to theme all the nodes individually then it’s a bit complicated process. While looking for alternatives to this, the following snippet work fine, this has been implemented in www.vinrcorp.com you can see the example before using it. The usage of the snippet is also quit simple just put this code into the header part or where ever you want, of page.tpl.php file of your theme.

Only local images are allowed.
	if ($node->nid == 1) {
	print 'image-1.jpg" />';
	}elseif ($node->nid == 2){
	print 'image-2.jpg" />';
	}elseif ($node->nid == 3){
	print 'image-3.jpg" />';
	}elseif ($node->nid == 4){
	print 'image-4.jpg" />';
	}elseif ($node->nid == 5){
	print 'image-5.jpg" />';
	}elseif ($node->nid == 6){
	print 'image-6.jpg" />';
	}elseif ($node->nid == 7){
	print 'image-7.jpg" />';
	}elseif ($node->nid == 8) {
	print 'image-8.jpg" />';
	}elseif (($node->nid == 9) | ($node->nid == 10)){
	print 'image-9.jpg" />';
	}elseif ($node->nid == 11) {
	print 'image-11.jpg" />';
	}else {
	print 'default-image.jpg" />';
	}

To use it just put images in the image folder and mention the path in the code and also replace the names of images as per the node ids. This will help you to display different banner images for different nodes.
I think you can use it and this works for you too. You can reply to this post for further help.

Vivek Dubey