:Hi. Commons is our shared, free media repository. Thus, images with a free license should be on Commons rather than on a specific wikipedia, as this benefits all wikipedias and users beyond. That said, there are a lot of exceptions, specific to individual wiki(m|p)edia projects. Some projects have decided not to store local images at all, and use Commons exclusively. Most, like en.wikipedia, allow either. Some files cannot be transfered to Commons at all, for example, fair use images from en.wikipedia or Panoramafreiheit images from de.wikipedia, and thus have to remain locally stored. And yes, the official namespace for images is "File:", with "Image:" still working as an alias.