Section 107.13 requires a person operating a civil small unmanned aircraft for flight to comply with the registration rules that section points to. For almost every Part 107 aircraft, that means 14 CFR Part 48 and FAADroneZone. The recreational model is different, and the test exists to see if you imported it.
Every Part 107 aircraft, including the light ones
A 245-gram quadcopter flown under Part 107 must be registered before flight, even with nothing else attached. The recreational exception that can leave an aircraft under 0.55 pounds unregistered does not apply to Part 107. Adding a camera later can matter for Category 1 operations over people, because Category 1 includes everything attached in the 250-gram limit. It does not change the registration duty. The light aircraft was already required to be registered.
Each Part 107 aircraft is registered individually and receives its own number. Three drones means three registrations. A recreational flyer may register once and put that one number on every drone in a personal fleet. A remote pilot who "already had a recreational number" and then starts selling photos has not finished the Part 107 registration. The FAA's Remote ID page makes the same distinction: Part 107 pilots register each aircraft, and they enter the Remote ID serial number when they add the device. That serial number links the records. It does not replace the registration, and registration does not replace the broadcast. See Remote ID.
Five dollars and three years
Part 48 registration of a small unmanned aircraft used under Part 107 costs $5 and is valid for 3 years. Renew before the expiration. An expired registration means that aircraft is not legal to fly under Part 107 until it is renewed. Distractors shuffle the fee and the term: $25 for 3 years, $15 for 5 years, $5 for 1 year. The course figures, taken from Part 48 and the FAA registration page, are $5 and 3 years.
The registrant is the owner, and the owner must be at least 13. If the owner is younger, a person who is at least 13 registers it. That is not the remote-pilot minimum age of 16. A 16-year-old can hold the certificate and still need to look at who the registered owner is. Ages are separated on the age and medical page.
The mark on the aircraft
Section 48.205 requires the unique identifier to be legible on an external surface. Inside the battery bay was an old practice and it does not count. A photograph of the number in a binder does not count. Carrying the registration certificate in your pocket, with a blank airframe, does not count. A permanent marker, engraving, or a durable label on the outside is what the rule is describing, as long as it stays readable.
You still carry your remote pilot certificate and identification under §107.7 when you exercise remote-pilot privileges. That is the pilot document. The registration mark is the aircraft document. Showing one does not satisfy the other.
What registration does not authorize
A registered aircraft is not a permission slip to sell aerial photos. The pilot still needs a remote pilot certificate, or must be directly supervised by a current remote pilot who can take control immediately. The aircraft still needs Remote ID compliance unless it is inside a FRIA under the Part 89 conditions. The flight still needs airspace authorization when §107.41 applies. Registration is necessary and it is not the rest of Part 107.
Pilot currency is a 24-calendar-month clock under §107.65. Registration is a 3-year clock per aircraft. Renewing one does not renew the other. Recurrent training is the recurrent training page.