Golang图片验证码的使用

以下是一个简单的Golang程序，用于生成一个简单的图片验证码，并将其作为响应返回给客户端。

package main
 
import (
    "bytes"
    "image"
    "image/color"
    "image/png"
    "io"
    "log"
    "math/rand"
    "net/http"
    "strconv"
    "time"
 
    "github.com/golang/freetype"
    "golang.org/x/image/font"
    "golang.org/x/image/math/fixed"
)
 
func main() {
    http.HandleFunc("/captcha", captchaHandler)
    log.Fatal(http.ListenAndServe(":8080", nil))
}
 
func captchaHandler(w http.ResponseWriter, r *http.Request) {
    w.Header().Set("Content-Type", "image/png")
    width, height := 240, 60
    // 创建一张图片
    img := image.NewNRGBA(image.Rect(0, 0, width, height))
 
    // 创建一个点进行填充
    red := color.RGBA{R: 255, A: 255}
    white := color.RGBA{R: 255, G: 255, B: 255, A: 255}
    blue := color.RGBA{B: 255, A: 255}
 
    // 填充背景为白色
    for x := 0; x < width; x++ {
        for y := 0; y < height; y++ {
            img.Set(x, y, white)
        }
    }
 
    // 生成随机数
    rand.Seed(time.Now().UnixNano())
    code := ""
    for i := 0; i < 4; i++ {
        num := rand.Intn(10)
        code += strconv.Itoa(num)
        // 将数字画在图片上
        drawCode(img, width/5*i, red, num)
    }
 
    // 画一些干扰线
    for i := 0; i < 5; i++ {
        drawLine(img, red)
    }
 
    // 写入验证码
    drawCaptcha(img, code, blue)
 
    // 输出图片
    err := png.Encode(w, img)
    if err != nil {
        http.Error(w, err.Error(), http.StatusInternalServerError)
    }
}
 
func drawCaptcha(img *image.NRGBA, code string, blue color.RGBA) {
    point := fixed.Point26_6{
        X: (fixed.I(img.Bounds().Dx()) - font.MeasureString(code).Ceil()) / 2,
        Y: (fixed.I(img.Bounds().Dy()) - font.Metric('m').Bounds.Ceil()) / 2,
    }
    d := &font.Drawer{
        Dst:  img,
        Src:  image.NewUniform(blue),
        Face: basicfont.Face7x13,
        Dot:  point,
    }
    d.DrawString(code)
}
 
func drawCode(img *image.NRGBA, y int, red color.RGBA, num int) {
    for i := 0; i < 40; i++ {
        img.Set(i+rand.Intn(10)+y, rand.Intn(height/5)+y, color.RGBA{R: red.R, G: red.G, B: red.B, A: 255})
    }
    fontSize := 20.0
    font := truetype.NewFace(basicfont.TTF, &truetype.Options{
        Size: fontSize,
        DPI:  72,