Strange border on IMG tag

You can Simply Use div instead of img for background image , if you are not going to use src attribute anywhere.

<div class="logo"> </div>

otherwise src is required.

It's the default "special" border that appears when you use an img element with an a src attribute set to something that doesn't exist (or no src at all).

A common workaround is to set the src to a blank.gif file:

<img class="logo" src="blank.gif" />

I have to point out that it (in this case) makes no sense to use an <img> with background-image. Just set the src attribute and forget about background-image.