During WordPress theme development you will more then likely need to display some images that are located within your theme directory.
The location of the images folder can vary greatly. It really comes down to how you like to set things up.
Generally speaking if you were to have an images folder in the root of your theme you can link to it like so from your php files:
<img src="<?php bloginfo('stylesheet_directory'); ?>/images/your-image.png">