- 35×45 mm
- The standard passport photo size used by the UK, most EU countries, India, Australia, and New Zealand. At 300 DPI this corresponds to a digital image of 413×531 pixels.
- 300 DPI
- Dots per inch — a measure of print resolution. 300 DPI is the standard for photo-quality printing. An image with embedded 300 DPI metadata will print at the physically correct size on a calibrated printer without manual scaling.
- Biometric photo
- A standardised photograph taken under controlled conditions to support automated facial recognition. ICAO Document 9303 defines international standards for biometric passport photos including head position, background, expression, and lighting.
- Head height ratio
- The proportion of the total photo height occupied by the face from chin to crown. Most passport specifications require the head to occupy 70–80% of the photo height, with specific minimum and maximum millimetre values.
- Background colour spec
- The required background colour for an ID or passport photo, specified by the issuing authority. Common requirements are plain white (US passports), plain off-white or light grey (UK passports), or plain white (India).
- ICAO 9303
- The International Civil Aviation Organization standard for Machine Readable Travel Documents. Part 3 defines the biometric photo specifications that most countries' passport offices use as their technical baseline.