A method is provided for automatically adjusting a size of characters using a camera. The method includes receiving an image with characters; adjusting a focus of the image with characters and detecting a region and a size of characters in the image; determining whether the size of the characters in the image falls within a preset range; recognizing the characters in the image and displaying the recognition results, if the size of the characters falls within the preset range; and automatically adjusting a zoom ratio of the image and recognizing the characters in the resized image, if the size of the characters does not fall within the preset range.