Might be getting ready to chop them down or trim them. Saw them down the road a few months ago doing the same and the next day they cut down every tree on that street. They do this to prepare for the winter season.

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Unless we're talking about a historic or "specimen" tree that might contribute value to your property, they may just be assisting the Road/Highway and/or Utilities with identifying trees that may cause problems during storms, winter, etc.

"Since we're already there.." kind of deal.

Did these people identify themselves as being from the Assessor's office? And if you talked to them to find out who they were, did you ask them why they were taking pictures of the trees

Honestly, call the office and talk with them. There may be legit reasons…there may also be some technical reason for landscaping being taken into consideration…but I doubt it…and unless you are a forester, arborist, or logger you prob can’t adequately value a tree for wood value…and most trees have little value beyond firewood if not oak or black walnut.

The Ents have gotten away with not paying taxes for decades now... it's about time if you ask me.

The city sometimes assess trees near power lines and structures to see if they need to inject more growth hormones. If the trees have small metal circular tags on them then that could have been what they were up to!