Well, borders and outlines differ from each other in these aspects: The border is computed along with the width and height of the element or picture, while the outline is completely outside the picture. An outline may overlap the content, while a border usually doesn't. If a border is added to a picture, we draw an outline on the outer surface of the border. Lastly, the width and height of the picture might get affected by a border, while there are absolutely no changes to the image dimension because of an outline.