Send e-mail to Gmail with inline image using Python

It seems that following the gmail email template works:

* multipart/alternative
  - text/plain
  - multipart/related
    + text/html
      <img src="cid:msgid"/>
    + image/png
      Content-ID: <msgid>

Based on the example from email module docs:

#!/usr/bin/env python3
import html
import mimetypes
from email.headerregistry import Address
from email.message import EmailMessage
from email.utils import make_msgid
from pathlib import Path

title = 'Picture report…'
path = Path('TESTING.png')
me = Address("Pepé Le Pew", *gmail_user.rsplit('@', 1))

msg = EmailMessage()
msg['Subject'] = 'Report…'
msg['From'] = me
msg['To'] = [me]
msg.set_content('[image: {title}]'.format(title=title))  # text/plain
cid = make_msgid()[1:-1]  # strip <>    
msg.add_alternative(  # text/html
    '<img src="cid:{cid}" alt="{alt}"/>'
    .format(cid=cid, alt=html.escape(title, quote=True)),
    subtype='html')
maintype, subtype = mimetypes.guess_type(str(path))[0].split('/', 1)
msg.get_payload()[1].add_related(  # image/png
    path.read_bytes(), maintype, subtype, cid="<{cid}>".format(cid=cid))

# save to disk a local copy of the message
Path('outgoing.msg').write_bytes(bytes(msg))

To send msg via gmail:

import smtplib
import ssl

with smtplib.SMTP('smtp.gmail.com', timeout=10) as s:
    s.starttls(context=ssl.create_default_context())
    s.login(gmail_user, gmail_password)
    s.send_message(msg)

Python 2/3 compatible version

* multipart/related
  - multipart/alternative
    + text/plain
    + text/html
      <div dir="ltr"><img src="cid:ii_xyz" alt="..."><br></div>
  - image/jpeg
    Content-ID: <ii_xyz>

Based on Send an HTML email with embedded image and plain text alternate:

#!/usr/bin/env python
# -*- coding: utf-8 -*-
import cgi
import uuid
import os
from email.mime.multipart import MIMEMultipart
from email.mime.text      import MIMEText
from email.mime.image     import MIMEImage
from email.header         import Header    

img = dict(title=u'Picture report…', path=u'TESTING.png', cid=str(uuid.uuid4()))

msg = MIMEMultipart('related')
msg['Subject'] = Header(u'Report…', 'utf-8')
msg['From'] = gmail_user
msg['To'] = ", ".join([to])
msg_alternative = MIMEMultipart('alternative')
msg.attach(msg_alternative)
msg_text = MIMEText(u'[image: {title}]'.format(**img), 'plain', 'utf-8')
msg_alternative.attach(msg_text)

msg_html = MIMEText(u'<div dir="ltr">'
                     '<img src="cid:{cid}" alt="{alt}"><br></div>'
                    .format(alt=cgi.escape(img['title'], quote=True), **img),
                    'html', 'utf-8')
msg_alternative.attach(msg_html)

with open(img['path'], 'rb') as file:
    msg_image = MIMEImage(file.read(), name=os.path.basename(img['path']))
    msg.attach(msg_image)
msg_image.add_header('Content-ID', '<{}>'.format(img['cid']))

To send msg via gmail:

import ssl

s = SMTP_SSL('smtp.gmail.com', timeout=10,
             ssl_kwargs=dict(cert_reqs=ssl.CERT_REQUIRED,
                             ssl_version=ssl.PROTOCOL_TLSv1,
                             # http://curl.haxx.se/ca/cacert.pem
                             ca_certs='cacert.pem')) 
s.set_debuglevel(0)
try:
    s.login(gmail_user, gmail_pwd)
    s.sendmail(msg['From'], [to], msg.as_string())
finally:
    s.quit()

SMTP_SSL is optional, you could use starttls method from your question instead:

import smtplib
import socket
import ssl
import sys

class SMTP_SSL(smtplib.SMTP_SSL):
    """Add support for additional ssl options."""
    def __init__(self, host, port=0, **kwargs):
        self.ssl_kwargs = kwargs.pop('ssl_kwargs', {})
        self.ssl_kwargs['keyfile'] = kwargs.pop('keyfile', None)
        self.ssl_kwargs['certfile'] = kwargs.pop('certfile', None)
        smtplib.SMTP_SSL.__init__(self, host, port, **kwargs)

    def _get_socket(self, host, port, timeout):
        if self.debuglevel > 0:
            print>>sys.stderr, 'connect:', (host, port)
        new_socket = socket.create_connection((host, port), timeout)
        new_socket = ssl.wrap_socket(new_socket, **self.ssl_kwargs)
        self.file = getattr(smtplib, 'SSLFakeFile', lambda x: None)(new_socket)
        return new_socket

I think you need to add the following lines:

from email.mime.image import MIMEImage

body = MIMEText('<p>Test Image<img src="cid:testimage" /></p>', _subtype='html')
msg.attach(body)


img = MIMEImage(image.read(), 'jpeg')
img.add_header('Content-Id', '<testimage>')
msg.attach(img)

testimage should be replaced with a unique identifier