It's not a secret but it may not be widely known. Most web developers will include what's called an "alternate tag" with any pictures that they put up on a web site.
As you discovered, if you move your mouse pointer over an image but don't click on it (it's called hovering) you may see a text description appear.
Try this example. Move your mouse pointer over the image on the right hand side that says Magnum in red. You should see a box pop up that says Magnum Computers. You may have to move the pointer off the image and then back on to see it.
There are a number of reasons for this. Obviously it can be used to give a little more information to a picture on the screen. Or it can help identify the content of the picture(s).
It began as a way to provide information to the blind and visually impaired. They couldn't "see" an image on a web site but there are devices that read aloud the content of a page. These devices could read the alternate text provided for a picture.
Also, pictures can take a long time to load and display - especially on a slower connection. Some people choose to tell their browser not to display the pictures to speed things up. The alternate tag will then appear instead of the image itself.
You can also hover over a hyperlink (the underlined text that takes you to another web page). When you do that, you can see the location of the web page that you will go to if you click on the link. Sometimes advertisements (both images and links) will both display some text and show the location you will go to if you click on it
Try this example. Move your pointer over the red Magnum logo again but don't click on it. You should see the destination web page listed in the task bar at the bottom of your screen.
This can add a lot to your web surfing experience so be sure to hover over images to see if the web developer left any messages or to see where that link may take you.
Answered by Tech Expert Dan Hanson