JavaScript - insertar imagen en google app script

function sequenceNumberOnFormSubmit(e) {

    var record = addSequenceNumber();

	var timestamp = e.values[0];

	var name = e.values[2];

	var mail = e.values[5];

	var subject = "Te has inscrito con exito ";

	var plain_email_body = "¡Hola" + name + "!" +

					"\n\n" +

					"We have registered you request, sent on " + timestamp +

					"\n\n" +

					"To follow you status ask for the request number" + record;

  var html_body =  "<font face='arial' size='3'> Hola, " + name + ":" +

			      "<br/><br/>" +

                              "Tu registro se ha realizado el: <i>" + timestamp + "</i>" +

			      "<br/><br/>" +

			      "Tu número de inscripción es el <font color=\"red\"><strong>" + record + "</strong></font>" +

                              "<br/><br/>" +

                              "Recuerda guardar tu numero de inscripción, ya que este será tu número de participante en nuestra challenge." +

                             "<br/><br/>" +

                             "Gracias," +

                             "<br/>" +

                             "La Organización.</font>";

	var advancedOpts = { name: "IPA Challenge", htmlBody: html_body };

	MailApp.sendEmail(mail, subject, plain_email_body, advancedOpts);

}

function addSequenceNumber() {

	// Obtain the sheet where we save the answers

	var sheet = SpreadsheetApp.getActiveSheet();

	// Obtain the last row with data

	var row =  SpreadsheetApp.getActiveSheet().getLastRow();

	// Sequence number (record) minus 1, this is due to the headers

	var record = row - 1;

	// Set (or write) the sequence number in the cell specified, change number 4 for the rigth column

	sheet.getRange(row,13).setValue(record);

	// Return the sequence number

	return record;

}