getting multiple images when scrolling down a page

Question

I am using this code for scrolling to get the images but when I am scrolling down multiple images are displayed.

Please can anyone rectify issues, may be problem with if condition.

<script type="text/javascript"> 
$(document).ready(function(){ 
    $(window).scroll(function(){
        var WindowHeight = $(window).height(); 
        //if($(window).scrollTop()+700 >= $(document).height() - WindowHeight)
        if ($(window).scrollTop() >= ($(document).height() - $(window).height())*0.7){ 
            $("#loader").html("<img src='http://www.niharonline.com/photo/ajax-loader.gif' alt='loading'/>");
            var LastDiv = $(".as_country_container:last"); 
            var LastId  = $(".as_country_container:last").attr("id"); 
            var ValueToPass = "lastid="+LastId;             
            $.ajax({ 
                type: "POST",
                url: "http://www.niharonline.com/photo/getdata.php",
                data: ValueToPass,
                cache: true,           `enter code here`
                success: function(html){             
                    if(html){
                        LastDiv.after(html);          
                        $('.columns-block').masonry('reload');
                    }
                }
            });
        return false;
        }
    return false;
    });
});
</script>