An electronic device comprising: a housing comprising a first surface; a display exposed through a first region of the first surface; a light emitting unit comprising light emitting circuitry disposed in a second region of the first surface; an image device comprising image acquiring circuitry disposed in a third region of the first surface; at least one processor disposed within the housing and electrically connected with the display, the light emitting unit, and the image device; and a memory disposed within the housing and electrically connected with the at least one processor, wherein the memory stores instructions that, when executed by the processor, cause to the electronic device to: acquire a first iris image using the light emitting unit and the image device; generate a first template based on the first iris image, the first template comprising a pupil size of the first iris image; store, as a reference template in a template database, the first template; acquire a second iris image using the light emitting unit and the image device; generate a second template based on the second iris image, the second template comprising a pupil size of the second iris image; authenticate the second template by comparing the second template with the reference templates in the template database; and store, as an additional reference template in the template database, when the pupil size of the second template succeeded in the authentication does not correspond to a pupil size of at least one of the reference templates in the template database, the second template. a housing comprising a first surface; a display exposed through a first region of the first surface; a light emitting unit comprising light emitting circuitry disposed in a second region of the first surface; an image device comprising image acquiring circuitry disposed in a third region of the first surface; at least one processor disposed within the housing and electrically connected with the display, the light emitting unit, and the image device; and a memory disposed within the housing and electrically connected with the at least one processor, wherein the memory stores instructions that, when executed by the processor, cause to the electronic device to: acquire a first iris image using the light emitting unit and the image device; generate a first template based on the first iris image, the first template comprising a pupil size of the first iris image; store, as a reference template in a template database, the first template; acquire a second iris image using the light emitting unit and the image device; generate a second template based on the second iris image, the second template comprising a pupil size of the second iris image; authenticate the second template by comparing the second template with the reference templates in the template database; and store, as an additional reference template in the template database, when the pupil size of the second template succeeded in the authentication does not correspond to a pupil size of at least one of the reference templates in the template database, the second template. acquire a first iris image using the light emitting unit and the image device; generate a first template based on the first iris image, the first template comprising a pupil size of the first iris image; store, as a reference template in a template database, the first template; acquire a second iris image using the light emitting unit and the image device; generate a second template based on the second iris image, the second template comprising a pupil size of the second iris image; authenticate the second template by comparing the second template with the reference templates in the template database; and store, as an additional reference template in the template database, when the pupil size of the second template succeeded in the authentication does not correspond to a pupil size of at least one of the reference templates in the template database, the second template.