A semi transparent overly is one way to keep text readable over busy images (previous post). CNN uses a different one: black and colorful bars behind white text. The length of the bar varies with the length of the text that it covers.
It is easy to recreate this effect in PowerPoint. Here an example with an image from one of my favorite boulevards in Paris (image credit to jfgornet). You can go further and imitate the retro lettering tape using stock images like this one.
