Hotlink protection prevents other websites from directly linking to files on your website.  When sites link to your files, it uses your hosting resources. Hotlink protection doesn't stop other sites from using your images, only from linking to your site directly.

To enable Hotlink protection, first log into your cPanel. Under "Security", click on HotLink Protection:

The next page will display the different options for setting up Hotlink Protection:

• URLs to allow access:  This is a list of sites that are allowed to link to your content. This list will include your own site, plus any other domains you host. You can add more by adding another website onto the list.
• Block direct access for these extensions: Here you can list the extensions you want to block. By default, image extensions are blocked, but you can add more extensions if needed. For example if you have movies, you can block .wmv or .mpg from being hotlinked.
• Redirect request to this URL: This is optional. If you want to redirect anyone that hotlinks to your site, you can do so in here.

Once you are done, click submit. Always visit your site after enabling Hotlink Protection to make sure it did not effect anything on your website. You can Enable and Disable Hotlink Protection any time.