[Abstract] 3D localization from images is an useful capability for robots and cameras. One successful approach is to rely on visual SLAM techniques. Another approach, maybe more robust, is to use visual markers in the environment. In this paper a study about the accuracy of marker based visual 3D localization is presented, using AprilTags markers and the solvepnp algorithm in OpenCV library. The impact of distance to markers, number of markers, their position in the image on accuracy of the 3D estimated pose is experimentally measured and analyzed., This research has been partially sponsored by the Community of Madrid through the RoboCity2030-III project (S2013/MIT-2748), by the Spanish Ministerio de Economía y Competitividad through the SIRMAVED project (DPI2013-40534-R) and by the URJC-BancoSantander, Comunidad de Madrid; S2013/MIT-2748, https://doi.org/10.17979/spudc.9788497498081