$('#myfile').change(function() {

$('#previewImg').attr('src', 'file:///' + $('#myfile').val());

alert($('#myfile').val());

});

<img id="previewImg" src="image/preview.jpg" width="80" height="80" />

<form action="">

请选择图片: <input id="myfile" name="myfile" type="file"

onchange="showPreview(this)" />

</form>