JPG-Repair Toolkit allows you to recover data from corrupted NEF photos (JPEG). Nikon RAW photos (NEF) contain the raw, ‘undeveloped’ sensor data. JPG-Repair Toolkit can process multiple Nikon RAW files (NEF) files in batch.
Commonly Nikon RAW photos embed one or more JPEGs: a low resolution thumbnail, a medium resolution preview, and in many cases a full frame preview. I have seen NEF photos were a full frame JPEG was embedded even though the camera was set to shoot at a lower resolution! Using JPG-Repair Toolkit you can extract the full frame preview.
Technically JPG-Repair Toolkit does not repair NEF photos, it extracts JPEGs already embedded! Of course having undeveloped and unprocessed RAW data is probably preferable, the full frame JPEG is hardly worthless.
How to recover data from corrupted NEF photos using JPG-Repair Toolkit
Time needed: 1 minute, assuming you have downloaded JPG-Repair Toolkit.
Acknowledgements:
To determine signatures I examined RAW files taken from: http://www.rawsamples.ch/index.php/en/canon.
And also: https://www.wesaturate.com/.