Quote:If you receive an email that contains linked images, Outlook does not download those images automatically by default. You can change this behavior if you want, but there risks to doing so. Let’s take a look.

To be clear here, we’re not talking about messages that contain images as attachments or about message into which the sender has inserted images (since those work pretty much like attachments). We’re talking about images that contain URL links to images that are hosted online.

When you get a message that contains images, Outlook prevents the download of those images and shows you a message at the top of the mail.

Full reading: https://www.howtogeek.com/398897/how-to-force-outlook-to-download-images-if-youre-sure-its-a-good-idea/