Huh - who knew - ask and you shall receive.
FlightAware sent an email with the following info, when you click to upload a photo - you will get this page; flightaware.com/photos/upload
It says; Please do not upload images you do not own or photos with a watermark; they will be deleted.
Below that there is a link; ( License Agreement ) it is an agreement between you and FlightAware.
FlightAware Media License
Do not submit content you do not own (e.g., work belonging to someone else or that you found on the Internet).
Any submitted content must not infringe on the trademark, copyright, or patent rights of any third party. FlightAware has the right to moderate, modify, or delete any and all images or media without prejudice.
The owner/submitter of any content continues to retain ownership to the submitted content.
You grant FlightAware a worldwide, royalty-free, unlimited, irrevocable license to use, transmit, distribute, and sell any submitted content.