You can create a custom user-defined exception and use it as an action when blocking ads. This will block the image from loading and will not display an error or an access_denied message.
(exception.silent_denied
(contact)
(details " ")
(format " ")
(help " ")
(summary " ")
(http
(code "200")
(contact)
(details)
(format)
(help)
(summary)
)
)