Create media items using the file system
You can create media library items by copying or moving files into a Sitecore file system, typically the /upload directory. If you create directories and files in the directory specified by the value attribute of the /configuration/sitecore/sc.variable element in web.config with name mediaFolder, Sitecore will create corresponding media folders and media items under /Sitecore/Media Library in the Master database.
Sitecore only creates media items if ASP.NET raises file system events. Before creating the media files in the Sitecore file system, ensure the ASP.NET process is active by requesting a resource processed by ASP.NET, such as the home page.
Excessive file system activity can overwhelm the ASP.NET worker process. You can monitor the media import process in the Sitecore log file to determine if it completes. If importing media fails, try importing a smaller batch.
You can delete the files after Sitecore creates media library items from them.