"Anonymous cameras" would be those that are not noticeable by the criminal fraternity because I have no interest in using cameras as a determent only in capturing an image that can then be used to prosecute criminals.
CCTV manufacturers usually refer to these types of cameras as "covert cameras" but there are several big issues/limitations when using covert cameras:
1) Limited Resolution - most covert cameras will not go above 5MP resolution and due to the small size of covert cameras, the lenses & sensors are usually not the best quality.
2) Poor Night Performance - Again due to the small size of covert cameras there is no space for IR LEDs or an IR cut filter and also with very small sensors they perform very poorly in very dark areas.
3) Not for Outdoor Use - most covert models do not have IP-ratings high enough for them to be safely used outdoors which massively limits where you can install them.
Our usual go-to for a small, simple CCTV system is a Hikvision system. If you want something dark to be less visible at night then Hikvision does offer a range of grey & black cameras that might suit this requirement and they can be paired with a 7604(B) 4-channel NVR if you do not plan to go beyond 4 cameras or a 7608NI-I2/8P if you do plan to have more than 4 cameras.