iPin others: add image above theme

I’d like to know how to do this, regardless of theme:

I want to be able to add a large image, logo/special notice type image, above the space specified in given theme. A lot of themes give you space for only a small logo, and when you change that around, it shifts menu items, etc etc.

I thought it might belong in the header.php but can’t crack it. Also, not sure how this would affect mobile/responsive capability or if there is a way to make it more friendly…

Thanks! Site for reference: firstyearfarmer.com

Want to add container width logo above current logo.