Hi David,
Yes you are right, the alt="text" method only works with Internet Explorer. I should have mentioned it.
No, I have neither found nor sought a way to make it cross-browser compatible, and I have never tried substituting an image to the text in the <a title=" "> tag suggested by David Bartosik.
Interesting. Although I have always been aware of its existence, this is a tag I have never used.
What I have done, however, is to use (or misuse, if you prefer) a rather elaborate script, originally conceived for a menu, to display an image on mouse-over. For example on my own website:
http://users.beagle.com.au/calamitas/ click on "Introduction" in the menu and drag your mouse over the "Strategy" and "Time Scale"
buttons at the top left. I would not recommend this method. I was just being lazy when I did it, and didn't bother to look for simpler ways of doing this.
Remember, I'm still an amateur. LOL
Geoffrey