The thing is: Blur in an image captured by a security camera is just the same as blur in any photo taken with any still camera. Blur is caused either by bad focus, OR motion blur. Motion blur is likely what you're talking about, and is caused by movement of the subject (or the camera) during the exposure of that "frame". So it's not the number of frames per second that you're capturing, but the shutter speed for the individual frames that determines how susceptible the setup will be to motion blur caused by the bad guys' movements.
Most of us go with 15 frames per second because things don't usually move all that fast, and the motion doesn't need to look "smooth" when viewing the video. We just need to capture enough frames that we don't miss details necessary to get a positive "holds up in court" identification of the bad folks. Usually, still images taken out of the videos are what people end up using to get positive ID on the subjects.
So all of that was to say that what you really need to have if you're trying to eliminate motion-blur in the individual frames, is a relatively high shutter speed (short duration in which the subject can move and create a blurred image). Again, this is just the same as shooting still photos with any still photo camera. High shutter speeds freeze motion. Slow shutter speeds can give you "motion blur" unless the subject (and camera) hold nice and still for their portrait.
So then we come to the question: What should you set as the lowest shutter speed you'll allow?
But, as the old adage for photography says: "There's no free lunch in photography". And by that, we mean that everything is a tradeoff!
High shutter speeds freeze motion. So that's great. But high shutter speeds, of course, reduce the amount of light that reaches the image sensor. So that's not so great!
On the one hand, we want great low-light images. On the other hand, we don't want motion blur. High shutter speeds that freeze action starve the sensor of light. So you can't have everything! And we haven't even talked about aperture settings.
Small apertures (high f/numbers) give you better depth of field. So focus is sharper over a wide range of distances from the camera. But as with high shutter speeds, high f/numbers cut down on the amount of light reaching the sensor!
So for low-light photography, we're usually stuck with slow shutter speeds (susceptible to motion blur) AND small f/numbers (large apertures) which give you shallow depth of field (meaning that things cannot be in sharp focus except in a narrow range of distances from the camera). Bummer, dudes!!!!
Now, there's a third factor for exposure: Sensor "gain" or "sensitivity". In a still camera, you can select the ISO number for the sensitivity of the sensor. But again, there's no free lunch! When you turn the gain up so that you have high sensitivity to light, you also end up with higher "noise" in the image. Better sensors can give us lower noise and better low-light images. But the higher the number of "megapixels" they jam onto a sensor, the smaller those individual pixels (sensels) are. And smaller photosensors are less sensitive, and have lower "full well" values. So their dynamic range is worse, and they're not as sensitive to light. Another bummer!
Anyhow, you end up having to balance a number of factors and arriving at a tradeoff. The highest megapixel cameras may produce very sharp, clear, and detailed images in good strong daylight. But they may be awful at night (and guess when we often need to get good images)!
And this adds more complexity because while a 4K camera might cover a given area well enough to get good face ID in the daytime, that same camera might produce so much noise in the images at night that the video will be useless.
What most folks here have decided are the best bet as of this moment in time, are the 1080P Starvis Starlight cameras. These sensors are a good tradeoff for what the state of the art is right now. Yes, they're only 2 megapixels. But they do very well in dim lighting, allowing you to use somewhat faster shutter speeds to help freeze movement and eliminate motion blur. But being only 2 Megapixels, you may need more cameras than you thought to cover a large area with enough resolution to give usable face ID over that area and at the distances in question. So there's a whole art and science to choosing the cameras, the lens focal lengths, positions, etc. to get what is necessary.
And that gets to your question of how many cameras you'll eventually need. Probably a LOT more than you're imagining right now! Always get equipment to handle many more cameras than you think you're going to want. Believe me!
Finally, there are options regarding lighting. If you've got good light in the area, that helps immensely. And many cameras have built-in infra-red illuminators for night use. But my experience with the built-in illuminators is not so good. Even on good, reputable cameras. They usually light up a small spot in the center of the image, and that means that areas outside of that spot end up underexposed by the camera's auto-exposure. Some Wide Dynamic Range processing can help, but it's no substitute for good, even illumination.
Further, built-in illuminators attract bugs, and worse, because the light is being emitted from right next to (or surrounding) the camera lens, tiny particles, snow, rain, dust, bugs, spider-webs, etc., that are near the camera are brightly illuminated and wreck the overall image as well as triggering motion detection, etc. So the point here is that off-camera (separate) illuminators are often far better, even though the camera has built-in illuminators.
Then we get to motion-lights. The problem there, is that when they switch on, the camera will take a while to adjust to the brighter scene, or switch from black and white to color, etc. And in those seconds, you can easily miss out on getting that all-important face shot as the guy flees the scene or covers his face, etc. So always-on lighting may be a lot better.
And speaking of covering their faces: Always remember that the only thing it takes to defeat a security camera is wearing a hoodie or ball cap, etc., and not looking at the camera. So camera mounting positions are critical as well. Mount them up too high, and you will see my bald spot as I'm breaking into your car, but not my face. So all you know is some old guy stole your stuff!
Anyhow, there's a lot to think about. And that's why everyone recommends that you read the
Wiki and the
Cliff Notes here. It is worth reading a LOT before buying anything. Lurking here can pay off, and asking questions is great.
Sorry for the long post. And good luck!
