LocalStorage of RNG Image

I have created a random number generator connected to an array of images, one of these images are shown randomly to the user when they load the page.

I'm struggling to figure out how to put one of these images in local storage so the same image does not appear when they reload the page, I just do not know how to do it.

Here is my JSFiddle if you need it, I don't know how to show the images on these though I hope that doesn't cause issues: http://ift.tt/2pHv5uB

HTML

<img src="" width="305" height="312" id="myPicture" alt="some image">

JS

window.onload = choosePic; // Run Function When Website Runs
var myPix = new Array("./images/service2.png","./images/service3.png","./images/service4.png"); //Array of 3

function choosePic() {
    randomNum = Math.floor((Math.random() * myPix.length)); //Random Number Generator based on the number of pictures in array
    document.getElementById("myPicture").src = myPix[randomNum]; //Random Number with image is set in HTML
}