A photograph is a printed analog image, and a ______ is the peripheral…

Digitization is the process of converting an analog (continuous) signal -- such as a physical photograph -- into digital (discrete, numeric) data. A digitization device captures the analog input through a light source and a sensor, and an analog-to-digital converter (ADC) then encodes the captured signal into digital pixel values that a computer can store and process.

A scanner is built exactly for this task. It shines light onto the physical photograph; a sensor array (such as a CCD) picks up the light reflected from the photograph line by line; the ADC then converts that captured light into a digital pixel grid, producing a digital image file from the original analog photograph.

Contrast with the other options:

• Printer -- an output device: it takes existing digital image data and produces a physical printed copy; it has no light-sensor input stage to accept a photograph.

• Webcam -- an input device with its own live sensor: it continuously converts the scene currently in front of the lens into a streaming digital video signal; it does not take an existing printed photograph as its input.

• Camera -- an image-capture device: depending on its sensor type (film or digital), it records the scene present in front of the lens at the moment of exposure; it does not take an existing printed photograph as its input either.

A camera or webcam can technically be pointed at a printed photograph and capture a fresh picture of it, but that is a different operation: it creates a new capture of whatever scene currently sits in front of the lens, not a purpose-built digitization of that specific analog document. The scanner is the peripheral specifically engineered to digitize an existing physical photograph or document, which is exactly what this task requires.

Since the task is to convert an existing physical photograph into digital form using a light-source-plus-sensor-plus-ADC pipeline, the scanner is the device built for exactly that purpose.