github.com/dchest/captcha

package main
  
  import (
    "fmt"
    "github.com/dchest/captcha"
    "log"
    "net/http"
  )
  
  func main() {
    // 获取验证码 ID
    http.HandleFunc("/captcha/generate", func(w http.ResponseWriter, r *http.Request) {
      id := captcha.NewLen(6)
      if _, err := fmt.Fprint(w, id); err != nil {
        log.Println("generate captcha error", err)
      }
    })
    // 获取验证码图片
    http.HandleFunc("/captcha/image", func(w http.ResponseWriter, r *http.Request) {
      id := r.URL.Query().Get("id")
      if id == "" {
        http.Error(w, "Bad Request", http.StatusBadRequest)
        return
      }
      w.Header().Set("Content-Type", "image/png")
      if err := captcha.WriteImage(w, id, 120, 80); err != nil {
        log.Println("show captcha error", err)
      }
    })
    // 业务处理
    http.HandleFunc("/login", func(w http.ResponseWriter, r *http.Request) {
      if err := r.ParseForm(); err != nil {
        log.Println("parseForm error", err)
        http.Error(w, "Internal Error", http.StatusInternalServerError)
        return
      }
      // 获取验证码 ID 和验证码值
      id := r.FormValue("id")
      value := r.FormValue("value")
      // 比对提交的验证码值和内存中的验证码值
      if captcha.VerifyString(id, value) {
        fmt.Fprint(w, "ok")
      } else {
        fmt.Fprint(w, "mismatch")
      }
    })
    log.Fatal(http.ListenAndServe(":8080", nil))
  }