A procedure for the determination of the location of prostate implant seeds that are wholly overlapped in a projection view has been developed. The procedure mainly consists of a series of image processing and an in-house developed localization software based on a three-film technique. To verify the efficacy of the procedure, a simulation phantom was built and nine sets of simulation were performed. For the assessment of the location of the seeds in the phantom, three images, one in anterior-posterior direction and two others in oblique angles, were acquired and a series of image processing was applied to the images for the removal of unnecessary background and the improvement of imaging quality. In this study, three types were considered; first, when two seeds were overlapped in one of projection images, second, more than three seeds were overlapped in one of projection images, and the third, all images contained wholly overlapped seeds. The developed software separates wholly overlapped seeds by calculating the distance between seeds in each film. This software can provide valuable information for establishing effective quality assurance in permanent prostate brachytherapy.