Image Capture and Acquisition
Cameras
Camera capacity is quoted in megapixels (width × height ÷ 1,000,000). More megapixels only help if the lens and sensor resolve real detail; they also increase file size and storage needs. Optical zoom changes the lens and keeps full resolution; digital zoom crops and interpolates, so quality falls. At capture, exposure, white balance and ISO (higher ISO means more image noise) determine whether the file is usable later.
File formats from the camera
JPEG applies in-camera processing and lossy compression - convenient, small, already "baked". RAW keeps unprocessed sensor data for maximum editing headroom but needs conversion and is much larger. TIFF is used in scanning and high-end workflows.
Scanners
Distinguish optical resolution (genuinely measured) from interpolated resolution (software-guessed, adds no detail). Scan at the final printed size and target ppi: roughly 300 ppi for photographs, 300 ppi greyscale for OCR text, higher (1200 ppi and up) for slides and film you may enlarge.
Other sources and traps
Screenshots, stock libraries and web downloads are also "capture". Assume every found image is copyrighted until licence terms say otherwise; check attribution, model releases and permitted uses. Other reliable traps: claiming digital zoom improves quality, claiming interpolated scan resolution adds detail, and equating megapixels with sharpness.
Rule of thumb: capture once at the highest genuine quality you can afford and archive that master untouched. Convert and downsize only for a specific output afterwards - never enlarge a weak capture to rescue a job.