A computer-implemented image-processing method for marking plaque fluorescent reaction areas, comprising: emitting, via a first light emitter, natural light to a mouth region of a user; obtaining, via an image-capturing unit, a first RGB image corresponding to the mouth region; emitting, via a second light emitter, blue light to the mouth region; obtaining, via the image-capturing unit, a second RGB image corresponding to the mouth region; converting, via a processing unit, the first RGB image and the second RGB image into a first HSV image and a second HSV image respectively; obtaining, via the processing unit, a first average brightness value corresponding to the first HSV image and a second average brightness value corresponding to the second HSV image, wherein the first average brightness value represents the average brightness value of each pixel in the first HSV image, and the second average brightness value represents the average brightness value of each pixel in the second HSV image; comparing, via the processing unit, the first average brightness value and the second average brightness value to obtain a brightness value of each pixel of one of the first HSV image and the second HSV image, wherein the one of the first HSV image and the second HSV image has the smallest one of the first average brightness value and the second average brightness value; multiplying, via the processing unit, a brightness value of each pixel of the one of the first HSV image and the second HSV image that has the smallest one of the first average brightness value and the second average brightness value by a ratio of the first average brightness value to the second average brightness value and a predetermined parameter value to obtain a normalized image; converting, via the processing unit, the normalized image into a third RGB image, and determining pixel points corresponding to the plaque according to a red value, a green value and a blue value of each pixel of the third RGB image and a brightness value of each pixel of the normalized image; and marking the pixel points corresponding to the plaque in the third RGB image and displaying the pixel points corresponding to the plaque in the third RGB image through a specific color value. emitting, via a first light emitter, natural light to a mouth region of a user; obtaining, via an image-capturing unit, a first RGB image corresponding to the mouth region; emitting, via a second light emitter, blue light to the mouth region; obtaining, via the image-capturing unit, a second RGB image corresponding to the mouth region; converting, via a processing unit, the first RGB image and the second RGB image into a first HSV image and a second HSV image respectively; obtaining, via the processing unit, a first average brightness value corresponding to the first HSV image and a second average brightness value corresponding to the second HSV image, wherein the first average brightness value represents the average brightness value of each pixel in the first HSV image, and the second average brightness value represents the average brightness value of each pixel in the second HSV image; comparing, via the processing unit, the first average brightness value and the second average brightness value to obtain a brightness value of each pixel of one of the first HSV image and the second HSV image, wherein the one of the first HSV image and the second HSV image has the smallest one of the first average brightness value and the second average brightness value; multiplying, via the processing unit, a brightness value of each pixel of the one of the first HSV image and the second HSV image that has the smallest one of the first average brightness value and the second average brightness value by a ratio of the first average brightness value to the second average brightness value and a predetermined parameter value to obtain a normalized image; converting, via the processing unit, the normalized image into a third RGB image, and determining pixel points corresponding to the plaque according to a red value, a green value and a blue value of each pixel of the third RGB image and a brightness value of each pixel of the normalized image; and marking the pixel points corresponding to the plaque in the third RGB image and displaying the pixel points corresponding to the plaque in the third RGB image through a specific color value.