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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);
    });

<form id="form1" runat="server">
        <input type='file' id="imgInp" />
        <img id="blah" src="#" alt="your image" />
</form>