I know there are a few widget image upload plugins in the WordPress plugin repository, many of them ok, few of them "strange", using custom upload solutions, but I found that in all I've checked there was no support for the Customize section in WordPress. Which is a shame because we should use more and more this awesome feature in WordPress.
As you can guess, I made one my self and here it is. This is a simple plugin that let's you upload an image in a widget (using the standard WordPress media upload function) and, if you wish you can add a link as well. So you can use it as a banner Ad or to feature something cool on your site.