Hello Phillip,
I'm not sure if the latest firmware 9.x include a official way to include a image for the ticket page, but I know a workaround to include a image in the ticket page:
1. Upload image via upload botton in the captive portal editor
2. Log in to EWC via SSH
3. Enter the command "shell ", then ENTER
4. Enter the root password, now you got a linux shell (busybox) The uploaded image is stored somewhere under /var/controller/images/cp/vns/NUMBER/image.jpg (NUMBER depends on creation of the vns). You can use the "find" command to search for the right path
5. Create a logical link to the file or copy file to /var/controller/www/NtwkCfg/ Example: ln -s /var/controller/images/cp/vns/1/image.jpg /var/controller/www/NtwkCfg/image.jpg
6. Upload your customized ticket page (html, including tag)
This works in my setup, but if you update the firmware the link/file is deleted. Steps 5 to 6 have to be redone.
Best regards
Hartmut Sachse