该问题的解决方法是通过使用Canvas API将图像转换为base64数据，然后将其上传到服务器。以下是一个示例代码片段：

function convertImageToBase64(url) {
  return new Promise((resolve, reject) => {
    let canvas = document.createElement('canvas');
    let img = new Image();
    img.crossOrigin = 'anonymous';
    img.onload = function() {
      canvas.width = this.width;
      canvas.height = this.height;
      canvas.getContext('2d').drawImage(this, 0, 0);
      let dataUrl = canvas.toDataURL('image/jpeg');
      resolve(dataUrl);
    };
    img.onerror = function() {
      reject(new Error('Failed to load image'));
    }
    img.src = url;
  });
}

// Usage:
convertImageToBase64('https://example.com/image.jpg')
  .then(base64Data => {
    // Upload base64Data to server
  })
  .catch(error => {
    console.error(error);
  });