A user terminal apparatus comprising: a camera; a display; at least one processor; and at least one memory configured to store one or more computer programs configured to be executed by the at least one processor, the one or more computer programs including instructions for the at least one processor to: control the display to display a user interface, UI, for providing a payment screen, control the display to display, on the UI and in response to a user command for performing payment being received through the UI, a fixation UI for guiding a point at which a user stares and a guide image comprising an eye guide image and an iris guide image, the eye guide image comprising a shape that corresponds to the eye of the user and the iris guide image comprising a shape that corresponds to an iris of the user and having a size indicating a size of the user iris if the user iris were to be located at a position corresponding to a focal length of the camera, so as to enable the user to determine whether their eye is closer to or further from the user terminal apparatus than the focal length of the camera, obtain an image of the user through the camera, control the display to display the image of the user on an area of the UI where the guide image is displayed, and perform iris recognition in response to a difference between a size of an iris included in the image of the user and the size of the guide image being within a preset range. a camera; a display; at least one processor; and at least one memory configured to store one or more computer programs configured to be executed by the at least one processor, the one or more computer programs including instructions for the at least one processor to: control the display to display a user interface, UI, for providing a payment screen, control the display to display, on the UI and in response to a user command for performing payment being received through the UI, a fixation UI for guiding a point at which a user stares and a guide image comprising an eye guide image and an iris guide image, the eye guide image comprising a shape that corresponds to the eye of the user and the iris guide image comprising a shape that corresponds to an iris of the user and having a size indicating a size of the user iris if the user iris were to be located at a position corresponding to a focal length of the camera, so as to enable the user to determine whether their eye is closer to or further from the user terminal apparatus than the focal length of the camera, obtain an image of the user through the camera, control the display to display the image of the user on an area of the UI where the guide image is displayed, and perform iris recognition in response to a difference between a size of an iris included in the image of the user and the size of the guide image being within a preset range. control the display to display a user interface, UI, for providing a payment screen, control the display to display, on the UI and in response to a user command for performing payment being received through the UI, a fixation UI for guiding a point at which a user stares and a guide image comprising an eye guide image and an iris guide image, the eye guide image comprising a shape that corresponds to the eye of the user and the iris guide image comprising a shape that corresponds to an iris of the user and having a size indicating a size of the user iris if the user iris were to be located at a position corresponding to a focal length of the camera, so as to enable the user to determine whether their eye is closer to or further from the user terminal apparatus than the focal length of the camera, obtain an image of the user through the camera, control the display to display the image of the user on an area of the UI where the guide image is displayed, and perform iris recognition in response to a difference between a size of an iris included in the image of the user and the size of the guide image being within a preset range.