First you need to name your images in this format:
- headerimage_1.gif
- headerimage_2.gif
- headerimage_3.gif
Once you have done that paste the following code in your header.php where you would like the images to be displayed or in any other file.
<img src="http://image_folder_path/headerimage_<?php echo(rand(1,3)); ?>.gif" width="image_width" height="image_height" alt="image_alt_text" /
