Flask表单图像转换为base64字符串

我创建了一个Flask表单,可以在其中上传图像。然后我需要将该图像转换为base64字符串,但我总是得到相同的结果。 打印输出:

<FileStorage: '20190925_184412.jpg' ('image/jpeg')>
b''

以及代码

from flask import Flask, render_template
from flask_wtf import FlaskForm
from wtforms import FileField
from flask_uploads import configure_uploads, IMAGES, UploadSet
import base64
app = Flask(__name__)

app.config['SECRET_KEY'] = 'thisisasecret'
app.config['UPLOADED_IMAGES_DEST'] = 'uploads/images'

images = UploadSet('images', IMAGES)
configure_uploads(app, images)


class MyForm(FlaskForm):
    image = FileField('image')


@app.route('/', methods=['GET', 'POST'])
def index():
    form = MyForm()

    if form.validate_on_submit():
        filename = images.save(form.image.data)
        image_string = base64.b64encode(form.image.data.read())
        print(form.image.data)
        print(image_string)
        return f'Filename: { filename }'

    return render_template('index.html', form=form)