An image processing device includes: a biometric sensor; and a processor to execute a process comprising: detecting base points of a first and a second fingers; calculating a first standard point between one of the base points of the first finger and one of the base points of the second finger; calculating a second standard point on a bisector of an angle formed by a straight line passing through one of the base points of the first finger on an opposite side of the second finger and the first standard point and a straight line passing through one of the base points of the second finger on an opposite side of the first finger, and the first standard point; and applying an affine conversion to the palm image so that coordinates of the first and second standard points are converted into predetermined coordinates.