$('.a').change(function(e) {
    var _URL = window.URL || window.webkitURL;
    var file, img;
    if ((file = this.files[0])) {
        img = new Image();
        img.onload = function() {
            $('.img').attr('src', this.src);
            console.log(this.width)
        };
        img.src = _URL.createObjectURL(file);
    }
})

使用

<img class="img" src="" width="100" height="100">
<input class="a" type="file">