Retaining original filenames

Is it possible to configure Omeka such that the original filenames are preserved, rather than being renamed to such as 89jlfa9030r83208jfsdj.jpg?

Not really. To avoid duplication of filenames (e.g., two people upload different files named ‘photo.jpg’), we need the hash to keep them distinct.

The plugin (and the module for Omeka S) Archive Repertory is designed for that.