  The transition probability for a one-dimensional discrete symmetric random
walk under a reflecting barrier was once given by the method of images. [S.
Chandrasekhar, Rev. Mod. Phys. 15, 1 (1943).] However, several inconsistencies
have been reported when the method of images is applied in cases where a
reflecting barrier is considered, even after the exact solution has been
obtained. Here, we explicitly show that the method of images becomes applicable
if the image position is shifted.
