In this work we propose improvements to the preliminary investigation on position based watermarking by proposing an informed insertion approach. In addition, we see how these modifications bring even higher fidelity in comparison to the original work, and how the system may become reasonably robust to some common image processing operations. Regarding robustness, we show how the proposed system may have an unique approach when dealing with collusion attacks. Usually in watermarking systems, the information to be transmitted is related to the watermark sequence itself. In contrast, in position based watermarking, the information is given by the watermark position in the image. In the informed embedding method for position based watermarking introduced here, an optimization criteria to choose the best among the available positions is suggested, improving considerably the system' performance. We compare the improved system with the traditional spread spectrum method and obtain good results regarding both fidelity and robustness to different attacks.