If you got a huge header, you can try to show to different images each time a user loads your site. You can rotate as many images as you want. But here for example we are giving you a example of three images. Hope this helps some.
One Step Procedure:
Note: Do take backup of your theme before you try this.
01. First rename your images with a underscore like these:
02. Add this below code in your header.php file or the file where the code for your header image is placed:
<img src="http://path_to_images/headerimage_<?php echo(rand(1,3)); ?>.gif"
width="image_width" height="image_height" alt="image_alt_text" />
03. If you want to do with more images, change the number 3. That’s it.