How to Prevent Image Hotlinking through .htaccess

What is Hotlinking

Hotlinking is the process of displaying an image on a website by linking to the same image on another website. It is mostly occurs with images. In simple words suppose i want to show some gadget picture on my website so instead of uploading the picture on my website, i link this picture to someone website using source as http://someone.com/gadget1.jpg.