The newest versions of Mathematica's commands for exporting (and importing) graphics (and symbolic expressions and sounds and data of all kinds) are impressively easy to use. The command HTMLSave will even save whole notebooks as HTML, automatically generating GIFs for non-text expressions and graphics. (For some very nice examples of the results, see the collection of Mathematica-related materials at ScientificArts.)
But there is also another (older) way of using Mathematica to present scientific information on the web, and that's MathReader. MathReader is a free software application, downloadable from Wolfram Research Inc., and it can be designated as a helper application for a web browser.
MathReader displays Mathematica notebooks exactly as the Mathematica Front End does, and without requiring any change in the Notebook file format. One advantage for graphics is that animations can be started and stopped, or run fame-by-frame or at different speeds, just as in the Mathematica Front End. Also, Mathematica Input and Output cells can be copied from MathReader and pasted (as text) into Mathematica itself, or into other applications. The Mathematica command HTMLSave creates GIF files for many types of cells, and the text-data is no longer present in the file.
Relying on MathReader for putting Mathematica on the web has
some disadvantages, however. First, it requires the audience for
your web pages either to get and install a copy of MathReader, or
to have access to Mathematica itself. Also, the readers of
your pages must be willing and able to download fairly large files, because
the Notebook file format makes no provision for compressing the graphics.