Large and high-resolution images usually have a high commercial value. Thus they are very good candidates for watermarking. If many images have to be signed in a Client-Server setup, memory and computational requirements could become unrealistic for current and near future solutions. In this paper, we propose to tile the image into sub-images. The watermarking scheme is then applied to each sub-image in the embedding and retrieval process. Thanks to this solution, the first possible optimization consists in creating different threads to read and write the image tile by tile. The time spent in input/output operations, which can be a bottleneck for large images, is reduced. In addition to this optimization, we show that the memory consumption of the application is also highly reduced for large images. Finally, the application can be multithreaded so that different tiles can be watermarked in parallel. Therefore the scheme can take advantage of the processing power of the different processors available in current servers. We show that the correct tile size and the right amount of threads have to be created to efficiently distribute the workload. Eventually, security, robustness and invisibility issues are addressed considering the signal redundancy.