When I click on a tail number and its tracking page pops up, there is usually a thumbnail at the top with two links to the side: [registration] and [photos].
If it helps, the [photos] link *does *appear if you enter an N-number into the “Flight/Tail#:” window on the left.
But if you’re looking at a list of flights (for an airport or a/c type) and click on an N-number contained with a list, that’s when the link fails to appear.
It’s generating the flight’s tracking page slightly differently.