Because an HTML file contains only text, the graphics you see in Web pages ”and the multimedia you can access from Web pages ”are not exactly a part of the HTML source file itself. Rather, graphics are linked to the page in either of two ways:
Whether inline or external, the media files you use in your Web pages challenge the browsers that are used to view your page. The browser must be capable of displaying graphics to display inline graphics. External media files can be played by either the browser or, more commonly, helper applications (or plug-ins) opened by the browser.
When choosing to incorporate media into your page, you have to consider carefully the file types you use. The text-only rule of HTML files is what allows users of many different types of computers to access Web pages. Graphics files are less likely to be readable by a wide range of systems, and sound and video files, even less so. Even within the confines of PCs and Macintoshes, you need to consider whether your media will be supported by a broad spectrum of browsers or helper applications.