pixels: a minute area of illumination on a display screen, one of many from which an image is composed.
image resolution : is the detail an image holds. The term applies to raster digital images, film images, and other types of images. Higher resolution means more image detail. Image resolution can be measured in various ways.

Megabyte  :a unit of information equal to 2²⁰ bytes or, loosely, one million bytes

megapixel : a unit of graphic resolution equivalent to one million or (strictly) 1,048,576 (2²⁰) pixels.

gigabyte : a unit of information equal to one billion (10⁹) or, strictly, 2³⁰ bytes.

Jpeg : a format for compressing image files.

psd : PSD, which stands for Photoshop Document, is the default format that Photoshop uses for saving data. PSD is a proprietary file that allows the user to work with the images' individual layers even after the file has been saved.

white balance : the color balance on a digital camera.

histogram : a diagram consisting of rectangles whose area is proportional to the frequency of a variable and whose width is equal to the class interval.

aperture : an opening, hole, or gap.

shutter speed : the time for which a shutter is open at a given setting.

depth of field : the distance between the nearest and the furthest objects that give an image judged to be in focus in a camera.

bitmap : a representation in which each item corresponds to one or more bits of information, especially the information used to control the display of a computer screen.

exposure : is the unit of measurement for the total amount of light permitted to reach the electronic sensor during the process of taking a photograph. The two main controls your digital camera uses to control exposure are the shutter speed and aperture.

watermarking : mark with a watermark.

optical zoom : On a digital camera, optical zoom is a true zoom feature. It allows you to zoom in (or out) on the subject in the LCD or viewfinder.

digital zoom : Digital zoom is a function of a digital camera used to make the image seem more close-up. Digital zoom on a digital camera works the same as cropping and enlarging a photo in a graphics program.

light meter : Typically a light meter will include a computer, either digital or analog, which allows the photographer to determine which shutter speed and f-number should be selected for an optimum exposure, given a certain lighting situation and film speed.

image stabilization : Image stabilization (IS) is a family of techniques used to reduce blurring associated with the motion of a camera or other imaging device during exposure.

noise : Image noise is random (not present in the object imaged) variation of brightness or color information in images, and is usually an aspect of electronic noise. It can be produced by the sensor and circuitry of a scanner or digital camera.

Time lag : the time it takes from when you press the shutter button to when the camera actually records the picture.

Hot shoe : A hot shoe is a mounting point on the top of a camera to attach a flash unit and other compatible accessories.

fisheye : a wide-angle lens with a field of vision covering up to 180°, the scale being reduced toward the edges.

marco :  is extreme close-up photography, usually of very small subjects, in which the size of the subject in the photograph is greater than life size (though macrophotography technically refers to the art of making very large photographs)

telephoto : a lens with a longer focal length than standard, giving a narrow field of view and a magnified image.

wide angle : (of a lens) having a short focal length and hence a field covering a wide angle.

DSLR : A digital single-lens reflex camera (also called a digital SLR or DSLR) is a digital camera combining the optics and the mechanisms of a single-lens reflex camera with a digital imaging sensor, as opposed to photographic film.