Some weird issue with my file upload and jQuery Image height width and new Image()

Question

I am developing a system where in A user uploads a image and the JS checks whether minimum width is more than 75 or not.

When we first time upload the file, it alerts a BLANK one. On selecting a next file it alerts the result for the file which was selected before, let me explain below.

1. FIrst I select a Image with width more than 200px, it alerts BLANK / Null / No Data.
2. When i then select a Image with less than 200px, ideally it should alert false, but it alerts true ( The result for the file selected before).
3. Now to reverify the problem, I select a Image with more than 200px, ideally it should alert false, but it alerts false ( The result for the file selected before).

Can anyone clear this mess? I tried googling but didnt help.

My HTML

<input type="file" id="file" />

My JS :

var _URL = window.URL || window.webkitURL;
var wid;
$("#file").change(function(e) {
    var file, img,hei;
    if ((file = $('#file').prop('files')[0])) {
        img = new Image();
        img.onload = function() {
            wid = ((img.width) > 200) ? true:false;
        };
        img.onerror = function() {
            alert( "not a valid file: " + file.type);
        };
        img.src = _URL.createObjectURL(file);
    }
        alert(wid);
});