pip install Flask_Google_reCaptcha

from flask import Flask
from google_recaptcha_flask import ReCaptcha

app = Flask(__name__)
recaptcha = ReCaptcha(app)

app.config.update(dict(
GOOGLE_RECAPTCHA_ENABLED=True,
GOOGLE_RECAPTCHA_SITE_KEY="SUA SITE CHAVE",
GOOGLE_RECAPTCHA_SECRET_KEY="SUA CHAVE SECRETA"
))
recaptcha.init_app(app)

<form method="post" action="/submit">
    ...
    {{ recaptcha }}

    [submit]
</form>

@route("/submit", methods=["POST"])
def submit():

    if recaptcha.verify():
        print("SUCCESS") 
        
    else:
        print("FAILED")

RECAPTCHA_ENABLED = True
RECAPTCHA_SITE_KEY = ""
RECAPTCHA_SECRET_KEY = ""
RECAPTCHA_THEME = "light"
RECAPTCHA_TYPE = "image"
RECAPTCHA_SIZE = "normal"
RECAPTCHA_LANGUAGE = "pt-br"
RECAPTCHA_RTABINDEX = 10