From this page of our guide to Sniper Elite 4, you will learn where to find and how to destroy 3 cameras in the first mission of the game - San Celini Island. Camera sabotage is one of the optional objectives of the mission, although dealing with it guarantees experience points.
The first camera (M1.1) is in front of the entrance to the ruined tower. It's surrounded by objects that can explode and destroy it but you may as well destroy the camera directly (use suppressed ammo). If you want you can come closer and shoot it with your pistol (use the bushes by the road, located 30m away from the target).
The second camera (M1.2) is located in the south-east part of the island. You can easily use the suppressed ammo and destroy it from the ruined tower. The target would be within 120m distance. You can safely get to the tower via the seaside, after you eliminate the second officer.
The last camera (M1.3) can be taken care of when you decide to eliminate Schmidt (it's in front of his mansion, by the seaside). Once you kill him, you will still need to get close enough to his body to collect his documents.