Just a Simple 1 Image Plugin?

Hi guys

Could someone recommend a simple plugin that simply displays a single, hyperlinkable image in the widget area that you choose where the user can simply just choose to Upload the image they want to when they want to replace the old one?

Basically this widget is going to be like a large image below the header and nav which will have promotions on it for a charity, and as they’re not very tech-savvy a plugin this simple is what they would need so they can easily change the image.

Hope someone can help.

Thanks
Steve.