Edit in JSFiddle

var scale = 2;

var $magnifyingGlass = $('<div class="magnifying_glass"></div>');
var $magnifiedContent = $('<div class="magnified_content"></div>');
var $magnifyingLens = $('<div class="magnifying_lens"></div>');

//setup
$magnifiedContent.css({
    backgroundColor: $("html").css("background-color") || $("body").css("background-color"),
    backgroundImage: $("html").css("background-image") || $("body").css("background-image"),
    backgroundAttachment: $("html").css("background-attachment") || $("body").css("background-attachment"),
    backgroundPosition: $("html").css("background-position") || $("body").css("background-position")
});

//$magnifiedContent.html(innerShiv($(document.body).html())); //fix html5 for ie<8, must also include script
$magnifiedContent.html($(document.body).html());

$magnifyingGlass.append($magnifiedContent);
$magnifyingGlass.append($magnifyingLens); //comment this line to allow interaction
$(document.body).append($magnifyingGlass);

//funcs


function updateViewSize() {
    $magnifiedContent.css({
        width: $(document).width(),
        height: $(document).height()
    });
}

//begin
updateViewSize();

//events
$(window).resize(updateViewSize);

$magnifyingGlass.mousedown(function(e) {
    e.preventDefault();
    $(this).data("drag", {
        mouse: {
            top: e.pageY,
            left: e.pageX
        },
        offset: {
            top: $(this).offset().top,
            left: $(this).offset().left
        }
    });
});

$(document.body).mousemove(function(e) {
    if ($magnifyingGlass.data("drag")) {
        var drag = $magnifyingGlass.data("drag");

        var left = drag.offset.left + (e.pageX - drag.mouse.left);
        var top = drag.offset.top + (e.pageY - drag.mouse.top);

        $magnifyingGlass.css({
            left: left,
            top: top
        });
        $magnifiedContent.css({
            left: -left * scale,
            top: -top * scale
        });

    }
}).mouseup(function() {
    $magnifyingGlass.removeData("drag");
});

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