If someone is purposely not respecting your choice of subject for your observation, that is definitely not cool.
Identifiers should take a moment to read any notes or existing IDs made by the observer and respect those, but sometimes they do make mistakes (I know I have). In situations like that, politely reply to them about the subject of the observation, they’ll usually fix it if they see the notification. If they refuse to do so, you can flag the ID or comment or email email@example.com.
Cropping to the subject can definitely be helpful, but it’s not necessary, and sometimes showing an entire scene is interesting.
Marking a photo is OK, but do keep in mind that the photo might be used to train the computer vision model. A few marked photos here and there are probably not going to make a big difference, but in general I’d recommend against it. We’d love to eventually include a way to annotate a photo without altering the actual image, but that will be further down the road.