HTML and CSS Reference
5.2. Inserting Images in Your Documents
One of the most compelling features of HTML and XHTML is their ability to
include images with your document text, either as intrinsic components
of the document (inline images), as separate documents specially selec-
ted for download via hyperlinks, or as background to your document or
elements within the document. When judiciously added to the body con-
tent, imagesstatic and animated icons, pictures, illustrations, drawings,
and so oncan make your documents more attractive, inviting, and profes-
sional looking, as well as informative and easy to browse. You may also
specially enable an image so that it becomes a visual map of hyperlinks.
When used to excess, however, images make your document cluttered,
confusing, and inaccessible, and they unnecessarily lengthen the time it
takes for users to download and view your pages.
5.2.1. Understanding Image Formats
Neither HTML nor XHTML prescribes an official format for images.
However, the popular browsers specifically accommodate certain image
formats: GIF, PNG, and JPEG, in particular (see the following sections for
explanations). Most other multimedia formats require special accessory
applications that each browser owner must obtain, install, and success-
fully operate to view the special files. So it's not too surprising that GIF,
PNG, and JPEG are the de facto image standards on the Web.
Both image formats were already in widespread use before the Web came
into being, so there's lots of supporting software out there to help you
prepare your graphics for either format. However, each has its own ad-
vantages and drawbacks, including features that some browsers exploit
for special display effects.
The Graphics Interchange Format (GIF) was first developed for image
transfer among users of the CompuServe online service. The format has