from random import randint
 from PIL import Image, ImageDraw, ImageFont
 def get_random_color():
   # 随机颜色RGB
   return randint(120, 200), randint(120, 200), randint(120, 200) 
 def get_random_code():
   # 随机字符
   codes = [[chr(i) for i in range(48, 58)], [chr(i) for i in range(65, 91)], [chr(i) for i in range(97, 123)]]
   codes = codes[randint(0, 2)]
   return codes[randint(0, len(codes)-1)]
 def generate_captcha(width=140, height=60, length=4):
   # 生成验证码
   img = Image.new("RGB", (width, height), (250, 250, 250))
   draw = ImageDraw.Draw(img)
   font = ImageFont.truetype("static/font/font.ttf", size=36)
   # 验证码文本
   text = ""
   for i in range(length):
     c = get_random_code()
     text += c
     rand_len = randint(-5, 5)
     draw.text((width * 0.2 * (i+1) + rand_len, height * 0.2 + rand_len), c, font=font, fill=get_random_color())
   # 加入干扰线
   for i in range(3):
     x1 = randint(0, width)
     y1 = randint(0, height)
     x2 = randint(0, width)
     y2 = randint(0, height)
     draw.line((x1, y1, x2, y2), fill=get_random_color())
   # 加入干扰点
   for i in range(16):
     draw.point((randint(0, width), randint(0, height)), fill=get_random_color())
   # 保存图片
   img.save("static/captcha/" + text + ".jpg")
   return text + ".jpg"
 if __name__ == "__main__":
   for i in range(1000):
     generate_captcha()

@app.route('/get_captcha', methods=['GET'])
 def get_captcha():
   img_list = os.listdir("static/captcha")
   img = img_list[random.randint(0, 1000)]
  return os.path.join("static/captcha", img)

<script>
   function Change() {
     $.ajax({
       url: '{{ url_for('get_captcha') }}',
       async: true,
       type: "GET",
       success: function (data) {
         document.getElementById("captcha").src = data;
       }
     })
   }
 </script>