Once upon a time, in the days of yore, shortly before the Punic wars and just after the invention of water, the World Wide Web was just text. It languished until the popularity of Mosaic, which allowed graphics on this medium. Now, the entire point of the web as it first existed was basically hyperlinks, allowing one to jump from one topic to another, and not really needing to worry about which server one was on at the time.
Now, hyperlinks of text were indicated separately, generally with blue text and an underline, which allowed for the user to easily see which text was hyperlinked and which text wasn’t.
However, now that there were images as well, there also needed to be a way for users to tell whether an image was a hyperlink. So, images that were hyperlinks had a blue border around them, easily indicating that they were clickable.
But, once images were involved, one started having artists and designers caring about the look of a page. And those blue borders just looked awful. So, they made sure to override the browser explicitly and tell it to not place that border there.
Web users nowadays might not even realize that those borders would be there unless they’ve done web development. But by default in IE at least, an image that’s a hyperlink has that blue border around it, and you have to explicitly ask for it to be removed when coding a page.
And so, of course, every web site on the planet pretty much does so, just so that that blue border doesn’t show up, since it ruins the design of the page.
Now, this has the problem that people can no longer easily tell which images are hyperlinks and which images are just plain images. Often, navigation (in the form of hyperlinks) is done through a bunch of images, since images are attractive and can often present information better than plain text can. So, people click on images, expecting them to be links, since many images are in fact links.
Which leaves me, the poor web interface designer, in the position of trying to figure out how to communicate information to users that is best depicted graphically, while at the same time not confusing them that when they click on it, it doesn’t do anything.