Can't get "alt" tags to work

I'm trying to set up a tiny webpage for myself with links on it to administer some of the other sites that I administer. I have a link to each site, with a picture as the part to click on, instead of just text.

Some of the sites have a similar picture, so I want to put "alt" tags in, so when I hover over them, the name of the site will appear, so I know which one I am clicking on.

I think I've done everything right, and I can view the ALT tags on other websites (even this one, I can hover over the logo on the top left, and the name of the site will appear!) But I cannot view these tags on this page that I have put together.

The only difference I can see is that the file I am opening is prefaced with "file:////" while other sites begin with http://, so I tried copying to my web server, and I'm still not seeing the alt tags.

Any ideas?