Add WriteJPG option for jpeg format captcha

captcha.go

@@ -15,6 +15,7 @@ import (
 	"math/rand"
 	"strconv"
 	"time"
+	"image/jpeg"
 )
 
 const charPreset = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"
@@ -80,6 +81,12 @@ func (data *Data) WriteImage(w io.Writer) error {
 	return png.Encode(w, data.img)
 }
 
+// WriteJPG encodes image data in JPEG format and writes to an io.Writer.
+// It returns possible error from JPEG encoding
+func (data *Data) WriteJPG(w io.Writer, o *jpeg.Options) error {
+	return jpeg.Encode(w, data.img, o)
+}
+
 func init() {
 	ttfFont, _ = freetype.ParseFont(ttf)
 }

captcha_test.go

@@ -8,6 +8,7 @@ import (
 	"os"
 	"testing"
 	"errors"
+	"image/jpeg"
 )
 
 func TestNewCaptcha(t *testing.T) {
@@ -26,6 +27,15 @@ func TestSmallCaptcha(t *testing.T) {
 	}
 }
 
+func TestEncodeJPG(t *testing.T) {
+	data, err := New(150, 50)
+	if err != nil {
+		t.Fatal(err)
+	}
+	buf := new(bytes.Buffer)
+	data.WriteJPG(buf, &jpeg.Options{70})
+}
+
 func TestNewCaptchaOptions(t *testing.T) {
 	New(100, 34, func(options *Options) {
 		options.BackgroundColor = color.Opaque