Optical Sensor Type / Size: The size of sensor that a camera has ultimately determines how much light it uses to create an image. In very simple terms, image sensors (the digital equivalent of the film your father might have used in his camera) consist of millions of light-sensitive spots called photosites which are used to record information about what is seen through the lens. Therefore, it stands to reason that a bigger sensor can gain more information than a smaller one and produce better images.
Valid Video Pixels:
5MP, 12MP max
Resolution: HD is defined by specific resolutions at specific frame rates with a specific aspect ratio. Any camera with a resolution of more than a million pixels is by definition a megapixel camera. The lowest resolution in the megapixel range in the security market is around 1.3 megapixels, which provides 1280 x 1024-pixel resolution (or 1.3 million pixels), and we're already seeing security cameras with resolutions as high as 10 megapixels (3,648 x 2,752 pixels). The range of megapixel cameras continues to expand to accommodate various application requirements.
Digital Zoom: Some cameras offer a digital zoom, which is simply some in-camera image processing. When you use a digital zoom, the camera enlarges the image area at the center of the frame and trims away the outside edges of the picture. The result is the same as when you open an image in your photo-editing program, crop away the edges of the picture, and then enlarge the remaining portion of the photo.