Copyrights

The rules for Adobe stock contributor say, that you need to be the creator of the assets. So basically, you can't upload the pictures. The copyright owner is the photographer. You can assume, that the copyright in the great lines is everywhere in the world similar. So posting a picture of you, without the consent of the copyright owner, is not to be recommended. On the other side, the copyright owner would need to have your consent to post the pictures because you have a right to control your image.

Models sign for that a model release, and you will have to attach a model release to your submissions, even if you are both the creator and the model.

The laws may vary depending on your location, but here in the United States photos are automatically protected by copyright when they are taken.  There is a formal process to go through that has additional benefits, but I don't know the exact benefits honestly.

Yes, If there is recognizable people or things in a photo then you should check the box.  If you took a photo of yourself, fill out a model release with yourself as both the photographer and model.  Like Nancy OShea mentioned, if someone else took the photo then the copyright belongs to them.

Something recognizable like a car as an example, still has IP rights owned by someone else so you'd need a property release from them if you wanted to use it's likeness commercially even though you may own the actual car

Just to cover the common reasons the "Recognizable Person or Things" box is checked, you'd also click the box if you are submitting artwork that you've created yourself.  If that is the case then you fill out the property release with yourself as the creator.  But this isn't particularly related to the question at hand.

Good luck!