1. An apparatus for estimating the number of objects in an input image, the apparatus comprising: a learning unit that calculates counted values of a linear regression function by learning an arbitrary image; a separation unit that separates a foreground region and a background region of the input image; an extraction unit that searches for features that require an amount of calculation that is below a particular threshold from features having high correlation with each other feature and extracts the features from the separated foreground region; and an estimation unit that estimates a number of objects in the foreground region as a dependent variable by allocating the counted values of the linear regression function that are calculated by the learning unit and the features that are extracted by the extraction unit as independent variables of the linear regression function.