Many WordPress themes place borders around images by default. This can be a problem in some cases -- for instance, your business logo may be circular, ... W3Schools.com: CSS Border; ...

The image's width will be 400 pixels wide because that's the value defined in the stretchX CSS class. Return to your document and change 400 to any other value to make the image stretch to that width.

Google's John Mueller said this morning in a webmaster hangout at the 20:55 mark that Google Image search does not index and rank images from CSS background code. He said if you want your images ...