ProtonMail supports encrypted embedded images, which allows you to insert images directly into a messages body along side the body text. This allows you to compose and read emails that have images stored in the message instead of linked.
To compose a message with an embedded inline image you can simply drag and drop the image into the composer. By doing this, the image will load, and you will be asked if you want to add the image as an attachment, or if you want to embed it inside the message body. If you click on the “Inline” button, the message will be inserted inside the message body, where the cursor is, and it can also be seen as an attachment:
With the support for embedded images, there is an additional setting under Settings>Account which enables you to load the embedded images automatically or manually, just as it was the case with images from outside sources. If you have this option set to manual, you will need to click on the “Show embedded Images” link inside the message, for the images to show.
This setting is different from the Show Images option, which affects images inserted with the “Insert Image” button, or received messages from outside sources (images linked from URLs).