In my Sharepoint masterpage I have added an `<img>` to the top of the `<body>` of the page so that I can use some CSS to set the `<img>` to fill the screen. 

However I want a different image to be displayed depending on the theme in use. I currently use the following inside the masterpage: 

```
<img alt="" id="fullscreen" src="/_layouts/images/Background.png" />

```

Is it possible to capture the name of the theme in use and append that to the file name so I can simple adjust file names to match there theme?

Or failing that can I add something to src=" " that will make the URL theme specific?