Pictures cannot be shown but shown as red X – Microsoft Outlook

When you open an email message that contains images in Microsoft Office Outlook, the image areas are blocked. These areas display a red X placeholder. Additionally, the images are sent or received as email attachments. Resolution. To resolve this problem, make sure that the Temporary Internet Files folder is valid.

https://learn.microsoft.com/en-us/previous-versions/troubleshoot/outlook/pictures-not-displayed-and-shown-as-red-x