Thunderbird's remote image blocking feature is a good way to protect yourself from possible contamination from viruses as well as protect you from spammers who are trying to capture your email address. This preference is on by default in Thunderbird and is set to allow the display of remote images from people in your personal address book. You can change this option by going to Tools | Options | Advanced, where you see a dropdown box that allows you to select the address book you want to use to manage who can send you remote content.
As shown in Figure 11-4, Thunderbird lets you know when it has blocked images by issuing an alert at the top of the mail message (similar to the alert Firefox uses to warn you about popups that have been blocked). If you view the email message and decide you want to see the content, you can simply click Show Images to see the images that have been blocked. Note that after you click this option, there is no way to undo this action, so be certain that you really want to see the images before you click Show Images.
Figure 11-4. Thunderbird's remote image blocking feature in action.