How do I authenticate a domain user to be able to use a network location as an image src?

I have an image with the src located on a network like so

<img src="//networkpath/image/image.png" />

The image renders just fine while debugging in visual studio, but it doesn't show once I publish.

I'm guessing it's an authentication issue with IIS, but I can't figure out what to change.

If I put that same code in a standard html file and run it locally in a browser, the image shows just fine.

Any suggestions?

Thanks