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function preview_image(event) {
    var reader = new FileReader();
    reader.onload = function () {
        var output = document.getElementById('user_thumbnail');
        var fileuploadIcon = document.getElementById("file_upload_icon");
        output.style.backgroundImage = "url('" + reader.result + "')";
        output.firstElementChild.style.display = "none";
        fileuploadIcon.style.marginTop = "45px";
    }
    reader.readAsDataURL(event.target.files[0]);
}