There are various examples on this website of repairs of half grey or truncated JPEG images. In those cases all image data is actually present, but due to an error or corruption only a part of it is visible. If data is simply missing because for example the file is partially overwritten or cut-off, repair is impossible.
Modern high resolution JPEGs often embed a reasonably sized preview JPEG. Merging the available part of the full resolution JPEG with the embedded preview can lead to acceptable results. Although not able to compete with an actually repaired photo, something is better than nothing.
Steps to repair half grey / truncated JPEG with embedded preview:
- Extract Preview from corrupt JPEG using JPEG-Repair
- Open both truncated file and extracted preview in photo editor
- Resize preview to match dimensions corrupt file
- Select intact part corrupt image
- Paste selected part into preview image
Exact steps depend on the photo editor you prefer to use. I use Paint.net (free). For extracting the embedded JPEG from the truncated JPEG I use JPEG-Repair.
With regards to JPEG-Repair: Use the extract tool to get the embedded preview JPEG. of course, the larger the preview, the better the result you can expect. It will never be able to complete with the original or an actual repair. So in case of half grey and truncated JPEG files, always try repairing it first.
Reasons for missing data:
- File is partially overwritten (JPEG-Repair will most likely show low entropy for the file data)
- File is truncated (size considerably smaller than similar intact files)
In this video I demonstrate this repair method: