Make JPG image stick to bottom of webpage without stretching

Hey guys I'm trying to get an image to stick to the bottom of my website. I can get it to stick to the bottom but then it stretches... This is my code:

<style>
    img {
      position: fixed;
      bottom: 0;
    }
</style>
<img src="fire.jpg" width="100%" height="100%" />

Instead of nicely sticking to the bottom of my webpage and changing dimensions as the webpage changes it's size, it just stretches around. All other Stack Overflow tips just do the same. Any help is appreciated.