1. An apparatus for measuring 3-dimensional positions of objects, the apparatus comprising: an image capturing module that acquires an image including an object; a detecting module that detects the object from the image acquired by the image capturing module and calculates sizes and coordinates of the object within the image; and a position calculation module that calculates the 3-dimensional position of the object in the space in which the object is positioned by using the following equations: 
 Z d =( F s ×I x )÷(2 ×F x ×tan(θ x )) 
 X d =(2 ×Z d ×tan(θ x )× D x )/ I x 
 Y d =(2 ×Z d ×tan(θ y )× D y )/ I y where X d , Y d , and Z d represent 3-dimensional coordinates within the space in which the object is positioned, F s represents a reference horizontal size of the object stored in the position calculation module, F x represents a horizontal size of the object within the image, I x represents a horizontal size of the image, I y represents a vertical size of the image, θ x represents a horizontal angle of view of a camera used by the image capturing module to acquire the image, θ y represents a vertical angle of view of the camera, and D x and D y are 2-dimensional coordinates of the object within the image.