If the venue images are not appearing on your splash pages when connecting to the hotspot gateway then double check that ALL of the walled garden entries are correctly entered in your hardware.
Missing images are typically caused by assets.smartwifiplatform.com or cloudfront.net not being entered into the walled garden. Additionally if you linked an external image when creating your splash page you will need to allow that domain in the walled garden.
You can get the latest list of Default walled garden entries here.