In header.php file of my WordPress theme, I have the following code to display a different header image for different pages.

<?php
  if (is_page('about')) {
      $image = 'image_about.jpg';
  } else if (is_page('projects')) {
      $image = 'image_projects.jpg';
  } else if (is_page('services')) {
      $image = 'image_services.jpg';
  } else if (is_page('contact')) {
      $image = 'image_contact.jpg';
  } else {
      $image = 'image_default.jpg';
  }
?>

<div id="header">
<img src="<?php echo bloginfo('template_url'); ?>
/images/<?php echo $image;?>" 
alt="<?php bloginfo('name'); ?>" />
</div>