The correct answer is 'Incorrect security settings in the email client'. This option is likely correct because email clients often have security settings that block images from unknown sources to protect the user from potential threats. Embedded images can sometimes be used for tracking or can act as a delivery mechanism for malware. If these security settings are too stringent, they might prevent all images from displaying by default. The other options are less likely: 'Incorrect settings in the host-based firewall' isn't typically responsible for blocking images within emails but rather for controlling network traffic. 'Incorrect settings in your email proxy server' could potentially cause issues with email delivery, but it is less likely to specifically block images within the emails. 'Incorrect settings in your web browser's trusted site configuration' affects how websites are displayed and trusted by your web browser, not how email clients render emails. Lastly, 'Incorrect email settings in the anti-virus software' might block attachments or scan them for malware, but it is generally not responsible for blocking images within the email content itself unless specifically configured to do so.