Sending Mailgun inline images in HTML using Python query library

I'm having problems with how I can send multiple inline messages using Apache Mailgun from a Python application using a query library. I currently have (using jinja2 for templates and flasks as web graphics hosted on Heroku):

def EmailFunction(UserEmail):
    Sender = 'testing@test.co.uk'
    Subject = 'Hello World'
    Text = ''
    name = re.sub('@.*','',UserEmail)
    html = render_template('GenericEmail.html', name=name)
    images = []
    imageloc = os.path.join(dirname, 'static')
    images.append(open(os.path.join(imageloc,'img1.jpg')))
    images.append(open(os.path.join(imageloc,'img2.jpg')))
    send_mail(UserEmail,Sender,Subject,Text,html,images)
    return html

def send_mail(to_address, from_address, subject, plaintext, html, images):
    r = requests.\
        post("https://api.mailgun.net/v2/%s/messages" % app.config['MAILGUN_DOMAIN'],
            auth=("api", app.config['MAILGUN_KEY']),
             data={
                 "from": from_address,
                 "to": to_address,
                 "subject": subject,
                 "text": plaintext,
                 "html": html,
                 "inline": images
             }
         )
    return r

Thus, the letter is sent normally, but at the end of the letter there are no images. When I click to download them, they are not displayed. Images are specified in HTML according to the api mailgun (simplified, of course!);

<img src="cid:img1.jpg"/>
<img src="cid:img2.jpg"/>
etc ...

Obviously, I am doing something wrong, however, I tried to link them using the request.files object, which did not even send an email and did not give any errors, so I assume that this is the wrong option.

, .

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