A picture is worth a thousand words. Unfortunately this is an understatement, and it is often actually more like the equivalent of 50,000 words, or 250 KBytes. Thus embedding large pictures in pages of text is usually not a good idea. More typical is to include a small copy of the image in the document, with a hyper link to the larger version of the image. An example would be:
<A HREF=big_ben.gif><IMG SRC=little_ben.gif></A>In this case, it is an image little_ben.gif that has been given an anchor with a hyperlink to big_ben.gif. Mosaic will display the small image embedded in the page of text, and will only retrieve and externally display the large image big_ben.gif if the user should click on the small image.
Images such as the one described are called external images to distinguish them from embedded or inline images. Most WWW browsers use a separate viewer program to display external images. On UNIX systems, the most common external viewer program is XV. On Apple Mac's the external viewer is called JPEG View. On Windows PC's it is called LVIEW. Generally external viewer programs do not come bundled with the WWW browser, and you'll have to obtain one separately. Usually external viewers can display a larger range of images than the WWW browser itself can, though this is changing as WWW browsers become more sophisticated. More advanced clients such as netscape do not need an external viewer at all.