I'm using a [custom header](http://codex.wordpress.org/Custom_Headers) in my theme. My aim is to add an `alt` attribute to my custom header `img` element. My `img` element so far looks like this:

```
<img src="<?php header_image(); ?>" height="<?php echo get_custom_header()->height; ?>" width="<?php echo get_custom_header()->width; ?>" alt="" />

```

How can I get the alt text of the custom header image?