golang为图片加文字水印

package main

import (
	"fmt"
	"image"
	"image/color"
	"image/jpeg"
	"io/ioutil"
	"log"
	"os"

	"github.com/golang/freetype"
)

func main() {
	//需要加水印的图片
	imgfile, _ := os.Open("u=488179422,3251067872&fm=200&gp=0.jpg")
	defer imgfile.Close()

	jpgimg, _ := jpeg.Decode(imgfile)

	img := image.NewNRGBA(jpgimg.Bounds())

	for y := 0; y