I have dynamic graphics over an image but they won't line up, what am I doing wrong?

    img = ExampleData[ExampleData["TestImage"][[1]]];
    d = ImageDimensions@img;
    pt1=d/4;pt2={d[[1]]3/4,d[[2]]1/4};pt3=3d/4;pt4={d[[1]]1/4,d[[2]]3/4};
    
    MultiContourPolygon[polys_List] := Module[{contours = Append[#, First[#]]&/@polys}, 
    	{Polygon@Join[Join@@contours,Reverse[First/@contours]],Line[contours]}
    ]
    
    LocatorPane[
    	Dynamic[{pt1,pt2,pt3,pt4}],
    	Overlay[{Image[img,ImageSize->400], 
    		Graphics[{Orange, Opacity[.4], 
    			Dynamic @ MultiContourPolygon[{{pt1,pt2,pt3,pt4}, {{0,0}, {d[[1]],0},d,{0,d[[2]]}}}]},
    			ImagePadding -> 0, ImageMargins->0, ImageSize->400
    		]
    		}, Alignment -> {Left, Left}, ImageSize -> 400
    	]
    ]

![enter image description here][1]


  [1]: https://i.sstatic.net/f4P3q.png