The use of icons and digitized photographs requires greater sophistication, since these are graphic images.* You should probably stick to using JPG file formats, since the format is non-proprietary and most graphical Web browsers can display these images without calling up an external viewer.* As I understand it, file formats such as JPG, TIFF, etc., are just ways of representing the location and intensity of pixels. There are numerous utilities available for converting a graphic image in one file format into an image in another format, since these utilities are simply algorithms that transform data represented one way into data represented in another. In creating the Web site of the Metaphysics Research Lab, I made the mistake of assuming that any file format that could be directly displayed by my NeXT Web browser (OmniWeb) could be directly displayed by other Web browsers. OmniWeb can directly display TIFF files, but unfortunately, others couldn't. However, there are programs which can convert TIFF files to JPG files, and so I simply converted the TIFF files and anchored the result into my HTML documents.
HTML does have some limitations. It is not nearly as sophisticated a typesetting language as LaTeX , for example. Though it supports italic, bold, and and diacritical marks in various sizes, it does not support a wide variety of fonts, Greek symbols, logic symbols, mathematical symbols, music symbols, etc. However, there are ways to work around this limitation. By explaining how I was able to insert logic symbols, Greek symbols, etc., into web documents using my computer system, you may get an idea of how to do something similar on yours.
The NeXTSTEP operating system (which has now evolved into Mac OS X 10.x) is a Unix system with a graphical interface. It includes a nifty program called Grab which captures any selected region on the computer screen as a TIFF file (i.e., as a graphic), no matter what is displayed there and no matter which application program created the display. NeXTSTEP (MacOS X) also comes with NeXTTeX (TeXShop), an implementation of TeX and LaTeX for the NeXT (Mac) platform. LaTeX is a computer typesetting program and it takes a sourcefile containing special ASCII typesetting commands and produces a DVI (PDF) file. However, before printing, they can be examined with NeXT's TeXView app (now TeXShop), which displays all the pretty LaTeX fonts, Greek, logic symbols, etc., clearly on the screen in display PostScript (now in display PDF) at many different resolutions. So to create an icon or formula with logical symbols in it, I wrote and processed a simple LaTeX file, viewed it with TeXView, used the mouse to draw a boxed region around the displayed symbols, used Grab to capture that region as a TIFF file, converted that file to a JPG file using ToyViewer, and linked the JPG file into the HTML document as an `in-line image'.* So much of the power of LaTeX and other computer typesetting programs is not necessarily wasted when creating web documents in HTML.*
For those running Windows, there are similar tools for capturing material displayed to the screen as graphics files. One is called GrabIt and another Capture. They are both shareware (which means you have to register and pay for them), but neither is expensive (GrabIt is more powerful and so more expensive). Both are available via ftp from winftp.cica.indiana.edu and its mirror sites.