Preview an image before it is uploaded

 <form id="form1" runat="server">
        <input type='file' id="imgInp" />
        <img id="blah" src="#" alt="your image" />
    </form>
<script>
 function readURL(input) {
        if (input.files && input.files[0]) {
            var reader = new FileReader();
         
            reader.onload = function (e) {
                $('#blah').attr('src', e.target.result);
            }
            reader.readAsDataURL(input.files[0]);
        }
    }
 
    $("#imgInp").change(function(){
        readURL(this);
    });
</script>