However, before I dismiss this completely, I think from purely a research perspective we can try few things. We cannot selectively chose to hide/display but what we can do is render an image using url redirect. This image will be coming from an external server and you will have total control over what to send back. So, while constructing the message embed an image that gets bytes from external url like -
<img height="X" src="<URL that serves image>" width="Y" />
I haven't given it a try myself but I think at least Outlook will not block the display of such image.