Ambient Light - the available light not employed specifically for photography.
Background - the area behind the subject; it should be smooth, flat, and non-patterned to minimize unwanted detail; the background should be plain white or off-white.
Background Illumination - light that illuminates the background. The background should be uniformly illuminated to remove any shadows or other lighting effects that would otherwise interfere with clearly discerning the facial outline on the background.
Centering - the orientation of the facial region within the frame; head should be positioned such that the approximate horizontal mid-points of the mouth and bridge of nose lie on a vertical line at the horizontal center of the photo width; and a horizontal line through the center of the subject's eyes can be located between 56% and 69% of the image height from the bottom of the photo.
Composition - the content and organization of the image that is being captured for the photograph. In this context, the composition of the photograph must show a clear, front view and full face of the subject against a plain and neutral light color background.
Compression – the process of encoding an image using fewer bits than an unencoded representation would use through the use of specific encoding scheme; file size reduction by the removal of data determined by an algorithm to be of lesser importance to the content of an image.
Compression Ratio – quantifies the reduction in data-representation size produced by a data compression algorithm; a representation that compresses a 10MB file to 2MB has a compression ratio of 10/2 = 5, or 5:1.
Enhancement – the modification of an image's intensity values, usually to remove blemishes or improve appearance.
Exposure - in photographic terms, the product of the intensity of light and the time the light is allowed to act on the film or digital camera sensor. In practical terms, the aperture controls intensity or amount of light, and shutter speed controls the time.
Facial Features - the makeup or appearance of a subject's face or its parts, including scars, tattoos, etc.
Facial Region Illumination - the light that is incident on the subject's face. The face should be clearly illuminated with all physical features shown and no shadows that would otherwise obscure facial features.
File Size - the size of an image in digital photography, measured in kilobytes (KB), megabytes (MB), or gigabytes (GB). File size is proportional to its pixel dimensions; images with more pixels may produce more detail at a given printed size, but they require more disk space to store and are slower to print.
Graininess - the sand-like or granular appearance of an image. Graininess becomes more pronounced with faster film and the degree of enlargement. In digital imaging, graininess may occur as a result of printing an image, the pixel resolution of which is too coarse, or as a result of using a printer with poor dot resolution
Head Orientation - the positioning of the subject's head, specifically positioning the face to the full frontal position, eyes level and open. For those individuals who wear glasses, proper head orientation is crucial in avoiding unwanted glare from glasses. Even so, care should be taken to meet the required facial area and face centering guidelines when positioning the subject's head to remove the potential glare.
Incandescent Illumination – conventional light bulbs.
Lens - one or more pieces of optical glass or similar material designed to collect and focus rays of light to form a sharp image on the film or digital camera sensor.
Lighting Arrangement - the lighting arrangement for subject illumination which should consist of a minimum of 3-point balanced illumination; two (2) points of illumination should be placed at approximately 45 degrees on either side of the subject's face, the third point should be placed so as to illuminate the background uniformly.
Neutral Expression - The subject's expression should be natural and expressionless, with both eyes open.
Over-exposure - refers to a condition where too much light reaches the film or digital camera sensor, either because it is too bright or has been applied too long, resulting in a very light photograph.
PPI - short for pixels per inch; the measurement of resolution based on sampling frequency.
Print - refers to an exposed film picture that is printed on photographic paper, in color or black and white. In digital imaging, a print is the result of printing the digital image on photographic-quality paper stock using a digital printer. For passport/visa photographs, the resulting print should measure 2 inches x 2 inches (51 mm x 51 mm).
Printing - producing the final photo of the captured image which should enable fine facial features to be discernable, whether the print results from conventional photographic processes or digital printout. The resulting print should exhibit a continuous-tone quality regardless of the print method used.
RGB - the way that the colors are recorded in digital imaging. A large percentage of perceivable colors can be represented by mixing red, green and blue (RGB) colored light in various proportions and intensities.
Red-eye - a photographic condition in which a subject's pupils appear bright red, caused by a direct reflection, through the pupil, from the retina of the eye when an on-camera flash is used. Red-eye is most noticeable when a subject's pupils have dilated (enlarged) to adapt to a darkened environment. The blood vessels in the retina create the bright red color. The effect can be minimized by several techniques, some of which are available in modern cameras. One of these techniques uses one of two quick pre-flashes immediately before the actual flash. The pre-flashes cause the pupils of the subject's eyes to constrict, thereby limiting the amount of light reaching the back of the eyes. A photographer can also minimize red-eye by turning on more room lights and taking photos under brighter lighting. Additionally, if an external flash unit can be detached from the camera, it can be placed slightly farther away from the lens.
Sampling Frequency – the number of samples (e.g., pixels) per unit (e.g., inch).
Subject Positioning - the position of the subject with respect to the camera; the subject should be placed in front of the background such that the focal distance from the camera's lens to the subject's face should be no closer than 4 feet (120 cm).
Three-Point Lighting Arrangement – balanced lighting arrangement consisting of two (2) points of illumination should be placed at approximately 45 degrees on either side of the subject's face, the third point should be placed so as to illuminate the background uniformly.
Under-exposure - refers to a condition where too little light reaches the film or digital camera sensor, either because the light is not sufficient or it hasn't been applied long enough; it results in a very dark photograph.
White Balance – color correction to conform to the viewing illuminant. Digital cameras use the White Balance setting to compensate for the color of different illumination sources by adjusting the balance among their three (red, green, and blue) color channels. For example, incandescent illumination (i.e., a conventional light bulb) provides much more red light than is present in daylight illumination and, consequently, under such lighting, the red channel values must be diminished relative to the green and blue values if neutral whites and grays are to be imaged without a reddish cast.