The problem is that the browser displays a border around this image. To remove the border in HTML/CSS, you need to change the required attributes. In this case you will have to set the attribute of ...

Many WordPress themes place borders around images by default ... Click "style.css" from the list of files on the right. Press "Ctrl-F," then search for "img" (without quotations).

HTML doesn't offer as clean a solution for vertical lines as it does for horizontal lines -- a vertical equivalent to the Set your image up within your text and add a "style" attribute tag.