1. A user terminal apparatus comprising: an imaging unit configured to generate an image of a user; a display configured to display the generated image; and a controller configured to: detect a user eye from the generated image, control the display to display a guide image in a position of the generated image in which the detected user eye is located, and perform iris recognition in response to a difference between a size of an iris included in the detected user eye and a size of the guide image being within a preset range.