1. Check the settings on your email client.
2. Make sure that your email client is downloading and displaying the images, as some clients prevent the download to save bandwidth or to protect your security.
3. Verify that the email is not set to be viewed in plain text instead of HTML.
4. Install or adjust the settings of any security software that may be preventing downloads.
5. Check to see if your email client has any other options that may be preventing the images from being downloaded.