Index.of Jpg 1001 How Do You Make It So People Cant Go To The "index Of.." Pages On Your Website?

How do you make it so people cant go to the "index of.." pages on your website? - index.of jpg 1001

In my website, if you currently www.myswebsite.com / pictures you take to a page called "index of images." I do not do that, but you can still go on each image to go www.myswebsite.com / images / image.jpg

Ideas?