Add image under navigation menu in Twenty Eleven Child

Do you want this image to be uploaded through the dashboard?

Not necessarily – I could also insert it into the root folder via ftp and take it from there. I am just not sure what php/css changes I need to do…

Which version of the theme are you using too?
If you create an “images” folder in your Child Theme and put your banner in there, you may just want:

<img alt="description of image" src="<?php echo get_stylesheet_directory() ?>images/your-banner.png" />

Thanks for your reply! I am creating a child of version 1.8 of the Twenty Eleven Theme.

I’m sorry, but in which .php do I put the code you suggested?

Header.php maybe, copy that file and paste it into your Child Theme folder.
Find this line:

</nav><!-- #access -->

Start a new line after that and put the code for your image.

I have added it into the Header.php as per your suggestion but only a large empty box appears with the image description in the top left corner. Perhaps I need to make some changes in style.css too to make it appear properly?

Maybe the path to your image is wrong

All sorted, thanks for your help!