thumbnail
The thumbnail KIO worker is used by for network transparent and persistent generation of thumbnails.
The thumbnail KIO worker uses plugins to generate the actual thumbnails. You can enable viewing of these thumbnails from the View Preview submenu, available in or in in file manager mode.
The thumbnail KIO worker is not directly useful to a user, but if you are a developer, you can use it within your own applications to create file previews.
Veja a documentação nos arquivos fonte para mais informações. Você encontrará isto na pastas thumbnail