Gmail will not render base64 images embedded inside HTML emails but with Google Apps Script, you can use blobs to send the base64 encoded images
Base64 is a way of encoding binary data (like images) as a string of text. This makes it possible to embed images in webpages and HTML emails without hosting images on a server. An issue however, particularly for email, is that not all email services like Gmail support base64 encoded images.
Amit Agarwal’s latest blog post discusses a workaround for Gmail which involves using Google Apps Script to convert the base64 images to a blob and then embedding the blob in the email. There are some nice techniques in this post for handling/searching text strings with regular expressions as well as converting them to a Gmail friendly format.