将图像从html canvas发送到flask python不起作用

<canvas id="myCanvas" width="400" height="300"></canvas>
<button onclick="sendImage()">发送图像</button>

<script>
function sendImage() {
  var canvas = document.getElementById("myCanvas");
  var dataURL = canvas.toDataURL(); // 将图像数据转换为Base64编码的字符串

  // 发送POST请求到后端
  fetch('/upload', {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json'
    },
    body: JSON.stringify({ image: dataURL })
  })
  .then(response => response.json())
  .then(data => {
    console.log(data);
  })
  .catch(error => {
    console.error('Error:', error);
  });
}
</script>

from flask import Flask, request
import base64
from PIL import Image

app = Flask(__name__)

@app.route('/upload', methods=['POST'])
def upload():
    data = request.get_json()
    image_data = data['image']

    # 解码Base64编码的图像数据
    image_bytes = base64.b64decode(image_data)

    # 将图像数据保存为文件
    with open('image.png', 'wb') as f:
        f.write(image_bytes)

    return {'message': '图像保存成功'}

if __name__ == '__main__':
    app.run()