Quick way too rename files for noobs.

Hi @makshmellow, you can use a Directory and File Pathnames (PATH) reader and a File Copy writer to add a common prefix to all JPG file names, which are saved under a specific directory and its subfolders.

1. Add a PATH reader and a File Copy writer for the same Dataset (a directory that contains subfolders containing JPG files) to the workspace, configure the reader/writer parameters as shown in the screenshots. You can also modify the parameters via the Navigator window after adding the reader and writer, if necessary.
2. On the Canvas, connect between {the PATH reader feature type and the File Copy writer feature type}, {source file path ('path_unix') and 'filecopy_source_dataset'}, and {source directory path ('path_directory_unix') and 'filecopy_dest_dataset'}. With a Windows machine, 'path_windows' and 'path_directory_windows' are also available.
3. In the File Copy writer feature type, set a string concatenating your desired prefix and 'path_filename' (i.e. original file name) to 'filecopy_dest_filename' (destination file name).

That's it.

Note: Since it would be so troublesome to restore the original file names if it failed, it would be strongly recommend to make a backup of the root directory and its descendant folders/files beforehand.