Responsive images

I want to implement the code for responsive images and have to place a snippet into the header:

<script>document.cookie='resolution='+Math.max(screen.width,screen.height)+'; path=/';</script>
.
What is the correct place for it within customizr?

If someone likes to know more about responsive images please visit the website e. g. of http://www.elmastudio.de/programmierung/mit-adaptive-images-bilder-fur-responsive-webdesigns-optimieren/
Quite interesting 😉