Edit in JSFiddle

 <label>
        Thumbanil Size :
    </label>
    <input id="txtThumbSize" type="text" style="width: 40px" value="64" />
    px<hr />
    <label>
        Select File To Create Thumbnail :
    </label>
    <input type="file" id="input" multiple onchange="thumb(this.files)">
    <hr /> 
  function thumb(files) {

        if (files == null || files == undefined) {
            alert("This Browser has no support for HTML5 FileReader yet!");
            return false;
        }

        for (var i = 0; i < files.length; i++) {
            var file = files[i];
            var imageType = /image.*/;

            if (!file.type.match(imageType)) {
                continue;

            }

            var reader = new FileReader();

            if (reader != null) {

                reader.onload = GetThumbnail;
                reader.readAsDataURL(file);
            }


        }
    }


    function GetThumbnail(e) {
        var myCan = document.createElement('canvas');
        var img = new Image();
        img.src = e.target.result;
        img.onload = function () {

            myCan.id = "myTempCanvas";
            var tsize = document.getElementById("txtThumbSize").value;
            myCan.width = Number(tsize);
            myCan.height = Number(tsize);
            if (myCan.getContext) {
                var cntxt = myCan.getContext("2d");
                cntxt.drawImage(img, 0, 0, myCan.width, myCan.height);
                var dataURL = myCan.toDataURL();


                if (dataURL != null && dataURL != undefined) {
                    var nImg = document.createElement('img');
                    nImg.src = dataURL;
                    document.body.appendChild(nImg);

                }
                else
                    alert('unable to get cntxt');

            }

        }

    }