Parse JSON array in javascript to pHp and mysql - no jQuery

I have a JSON Object getting a list of images I have on the page. The images are generated at random using a database. I want to keep adding to the images using AJAX whn the user for example clicks "show more". The images src are found so that no duplicates are pulled from the database on the AJAX call.

I want to know how to parse this array to the pHp file to perform an SQL statement to get more images to append to the images list. In the php file how would I select the elements from there. So SELECT * FROM images WHERE image_src NOT IN (JSON array) ORDER BY rand() LIMIT 12

CODE

var imageArray = {};
imageArray.itemList = [];

function imagesLoaded(){
    var gal_img_thumbs = document.getElementsByClassName("gal-thumb-image");
    for (var i = 0; i < gal_img_thumbs.length ; i++){
        var img = gal_img_thumbs[i].firstChild.getAttribute("src");         
        var new_obj = {'src':img};
        imageArray.itemList.push( JSON.stringify(new_obj));

        //imageArray.itemList.[i]['src']=img;
    }
}

function loadImages(){
    console.log("load images");
    if (window.XMLHttpRequest) {
        // code for IE7+, Firefox, Chrome, Opera, Safari
        xmlhttp=new XMLHttpRequest();
    } else { // code for IE6, IE5
        xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
    }
    xmlhttp.onreadystatechange=function() {
        if (xmlhttp.readyState==4 && xmlhttp.status==200) {
          document.getElementById("txtHint").innerHTML=xmlhttp.responseText;
        }
    }
  xmlhttp.open("GET","getimages.php?imgArray="+imageArray.itemList,true);
  xmlhttp.send();
}