You could be talking about two entirely different cases. '''Images can be embedded in the content of the email by the sender.''' In HTML, these images appear in the actual content and are not attachments. If viewing as plain text, then they will be removed from content, the alternative text will be displayed and the image will be presented as an attachment. For images embedded in messages: select setting: "View > Message Body As" and choose either "Original HTML" or "Simple HTML". If you are seeing what looks like an outlined box and this is an embedded image not remote content, it means the image file was not inserted correctly allowing the recipient to view the image. As an example in Thunderbird: Open new Write message click on the content area to get focus Insert > Image click on 'Choose file' to select an image file. Notice the 'attach this image to the message' check box. If you do not have this box checked, then you will discover that images will appear as a box - the image will not be attached. '''Images can be attached to the email by the sender.''' they are not embedded; not inserted into the actual content of the email; they have been attached. It is possible to allow attached images to display below the email by selecting: View > display attachments inline'. '''Images inserted as remote content:''' In HTML, the image has a pointer to a picture rather than embedding the actual picture in the message. The advantage is that the message is much smaller. The disadvantage is that the picture is physically on another server; if the image is available, you will see it. Some e-mail clients might be configured to block remote images. Thunderbird auto blocks remote content to safe guard your privacy. If the images were remote content and you are viewing using 'original HTML - not plain text, , you will see an alert below the header info saying: 'To protect your privacy, Thunderbird has blocked remote content in this message'. These images are replaced with an outlined box containing a broken file icon image.