Guide updated on 4 November 2026. It brings together and replaces the site’s articles on resolution, night vision, IP ratings, person and vehicle detection, false alarms, pet cameras and dummy cameras. For privacy rules, read the guide on cameras and the law.
Choose a camera by starting from a precise question: what do I need to see, how far away and in how much light? “Seeing someone walk into the garden” and “recognising the face of whoever rings the gate bell 6 metres away” call for very different cameras. Spec sheets push megapixels, but the lens, the sensor and night lighting matter at least as much.
1. The DORI method: how many pixels you need to recognise someone
The European standard EN 62676-4 on video surveillance defines four levels of detail, measured in pixels per metre of scene (the DORI method):
| Level | Pixels per metre | What it allows |
|---|---|---|
| Detection | 25 | Telling that a person or vehicle is there |
| Observation | 62 | Seeing what they are doing, general clothing |
| Recognition | 125 | Recognising someone you know |
| Identification | 250 | Identifying a stranger’s face or a nearby number plate with certainty |
Pixels per metre are worked out like this: scene width = 2 × distance × tan(horizontal angle ÷ 2), then pixels per metre = horizontal pixels ÷ scene width. Here are the maximum distances for each level, calculated with this formula for two typical lenses:
| Camera | Identification | Recognition | Observation | Detection |
|---|---|---|---|---|
| 2.8 mm wide-angle lens (about 100° horizontal) | ||||
| 2 MP (1920 px) | 3.2 m | 6.4 m | 13 m | 32 m |
| 4 MP (2560 px) | 4.3 m | 8.6 m | 17 m | 43 m |
| 8 MP / 4K (3840 px) | 6.4 m | 12.9 m | 26 m | 64 m |
| 6 mm lens (about 50° horizontal) | ||||
| 2 MP | 8.2 m | 16.5 m | 33 m | 82 m |
| 4 MP | 11 m | 22 m | 44 m | 110 m |
| 8 MP / 4K | 16.5 m | 33 m | 66 m | 165 m |
The table shows the key point: for the same megapixels, a narrower lens sees further but covers less area. A long driveway needs a 4–6 mm lens or a varifocal model; an entrance or small courtyard is fine with a 2.8 mm wide angle. These are theoretical values in good light: at night, with heavy compression or against the light, real detail drops.
2. Resolution: 2K, 4K and when you don’t need them
More pixels only mean more detail if everything else keeps up. A 4K camera with a small sensor often produces worse night images than a good 4 MP camera with a larger sensor. High resolution also weighs on the network and the recorder: more bandwidth, more disk space, slower streaming to your phone.
- 2 MP (1080p): enough for small indoor spaces and pet cameras.
- 4 MP (2K): the best compromise for most homes.
- 8 MP (4K): useful for large areas, when one camera must cover a lot, or for reading number plates at a distance with the right lens.
Also look at sensor size (1/2.8″ or larger beats 1/3″ or 1/4″ at the same resolution) and support for H.265 compression, which takes less space than the older H.264 for the same quality.
3. Night vision: infrared, white light and colour
| Technology | How it works | Pros | Cons |
|---|---|---|---|
| Infrared (IR) | Invisible LEDs light the scene; the image is black and white | Discreet, stated range often 20–40 m | No colour; insects and cobwebs in front of the lens cause false alarms; reflections off nearby glass and walls dazzle |
| White light (“colour night”) | A spotlight switches on and the camera records in colour | Colours of clothing and cars, deterrent effect | Visible; can bother neighbours if it points beyond your property |
| Low-light sensors | A very bright sensor and lens use existing lighting | Colour without spotlights, if there is some light | Cost more; total darkness still needs IR |
The stated IR range is the distance at which the scene is lit, not the distance at which you can recognise someone: the DORI table covers that. Never mount an IR camera behind glass: the LEDs reflect and the image turns white.
4. Outdoor cameras: what IP66 or IP67 means
The IP code, defined by IEC 60529, shows protection against dust (first digit) and water (second digit).
| Code | Dust | Water | Suitable for |
|---|---|---|---|
| IP65 | Dust-tight | Water jets | Sheltered outdoor spots, under a canopy |
| IP66 | Dust-tight | Powerful jets, driving rain | Exposed outdoor locations: the standard to look for |
| IP67 | Dust-tight | Temporary immersion up to 1 m | Places where water can pool |
The IP rating applies to the camera, not to the connections: protect cable joints with a waterproof junction box. Where a camera can be hit or vandalised, also look for IK10 (impact resistance), typical of dome cameras.
5. Person and vehicle detection: fewer false alarms
“Classic” motion detection compares one frame with the previous one: leaves, shadows, rain, headlights and cats trigger notifications all the time. Cameras with person and vehicle detection analyse the image with a trained model and only alert you when they recognise that shape.
- Draw a detection zone that leaves out the street, trees and plants moving in the wind.
- Use line crossing (tripwire) to be alerted only when someone comes in, not when they walk past on the pavement.
- Adjust the sensitivity after a week’s trial, looking at which events were useless.
- Check whether the analysis happens on the camera or in the vendor’s cloud: in the second case images leave your network and a subscription is often needed.
Facial recognition is another matter: it processes biometric data and has strict limits for private individuals, as the guide on cameras and the law explains.
6. Indoor and pet cameras
To keep an eye on a pet or your home while you are away, different things matter: a wide angle or a motorised pan-tilt head, two-way audio, good indoor night images and above all a physical shutter or privacy mode that switches the camera off when you are home. 2 MP is enough. Choose a vendor that updates firmware and allows recording to a microSD card, so the cloud is optional.
7. Are dummy cameras any use?
A dummy camera may deter an opportunist, but it records nothing: if something happens you have no evidence. People who watch a house before breaking in often spot dummies (no cable, a blinking red LED that real cameras don’t have). Today a real indoor camera costs little more than a fake one: one real, well-placed camera makes more sense than three dummies.
Checklist for choosing
| Question | What to look at |
|---|---|
| What do I need to see, and how far away? | DORI table: resolution + lens |
| Is there light at night? | IR, white light or low-light sensor |
| Is it outdoors? | IP66 or higher, IK10 if within reach |
| Do I want fewer useless notifications? | Person/vehicle detection, zones and lines |
| Where do I record? | NVR, card or cloud: see the guide on installing and recording |
| Is it secure? | Firmware updates, no mandatory cloud: see camera cybersecurity |
Sources
- EN 62676-4, video surveillance systems for use in security applications, application guidelines (DORI levels); values summarised by TP-Link, “What is DORI?”.
- IEC 60529, degrees of protection provided by enclosures (IP code).
- Distance calculations: ciaranfi.org, using the formula given in the text.