A photo of a billboard may well violate copyright as a technical matter. Whether there are damages, which is required for standing's injury in fact element, is a separate issue. Nonetheless, this is why you would often see apparel logos blured out on shows like cops back in the day.

A better analogy may be tubi. They allow anyone to watch movies available via their service for free, but that doesn't mean that you can scrape their database and keep copies on your computer.

The fediverse does have one feature that may cut the other way, and that's media proxy, where a server makes and keeps local copies of remote media. There is a counter argument that does align with my tubi example though. By using certain software, like pleroma, Instance operators have licensed their content to be used / copied via media proxy. That doesn't entail a global license to use copyrighted material for other purposes.

Just because I have a poast logo cached somewhere on my server doesn't mean that I can make and sell poast swag or otherwise use the material for purposes other than the purposes of federating poast.