An image doesn’t require a height attribute, but it has its
uses. The main use for specifying the width) is to improve the
user experience while a page is loading. If the dimensions are
specified in the markup, as the page is loaded, the space
required for the images is reserved by the browser; without this
information, the browser doesn’t know how big the image is, and
can’t allocate the appropriate space to it. On a slow-loading
page, the effect can be quite disturbing, as content is
constantly reflowed as each new image appears on the page. The
downside of specifying a width) is that if you later decide to
update an image that’s used site-wide—for example, a company
logo—you’d need to change the dimension attributes for each page
of the site. Depending on how your web site is managed
(manually, in a template-driven way, via a CMS, or through
server-side includes), this may either be a minor niggle, or a
real issue for you. It’s a case of weighing up the pros and cons
in each situation. height attribute is