Why HEIC files get corrupted, and how to recover them

Three things can be broken

'Corrupt' is one word for several different failures. The container's structure can be damaged, which breaks the file's ability to describe itself. The image data can be truncated, which breaks decoding partway through. Or the metadata can be malformed while the picture itself is perfectly intact.

Which of those occurred decides what is recoverable. A file with a bad metadata box may convert cleanly; a file missing half its image data will not produce a complete picture no matter what is done to it.

Separating these cases is the entire point of running a health check before reaching for a recovery tool.

Common causes

The first two items below account for most cases. A partial write produces a file that is structurally valid up to the point where it stops, which is why the damage often sits at the end of the file and the beginning still decodes.

• A transfer or download that stopped before it finished.
• The device losing power or being disconnected mid-write.
• Storage or filesystem errors on the card or disk.
• Software that exported the file incorrectly.
• A camera app force-closed while it was writing.
• A tool that edited the file in place and did not finish.

Diagnose before attempting recovery

Run the health check. It reports one of a small set of outcomes: healthy, readable with warnings, partially readable, cannot decode, not a HEIC, or unsupported feature. Each of those points at a different next step, and knowing which one applies stops you from wasting effort.

It also gives you a baseline. If a recovery attempt changes the outcome, you can tell whether it helped or hurt, which is not possible once you have overwritten the file.

Keep the report. When a file matters, a note of what the check said is more useful than a memory of which tools were tried and in what order.

Reading the outcomes

These categories describe your file, not the quality of any particular photograph. A partially readable result says nothing about how good the picture is, only about how much of it survived.

• Healthy: the file decodes and its structure is sound. If a tool still refuses it, the tool is the problem.
• Readable with warnings: the picture decodes, but something about the structure is unusual. Converting usually works.
• Partially readable: some image data decodes and some does not. Expect a usable but incomplete result.
• Cannot decode: the image data could not be turned into a picture, so recovery options are limited.
• Not a HEIC: the container brand says something else. Check the real format before going further.
• Unsupported feature: the file is valid but uses something the tool does not implement. Try another decoder.

What can often still be recovered

If the container is intact and only the metadata is malformed, the image itself may decode perfectly, and a conversion produces a usable file. If the image data is truncated, part of the picture may decode and part may not.

If the primary image is gone entirely, there may be nothing to recover. A missing image item is not something a converter can invent, and a tool that promises otherwise is reconstructing rather than recovering.

Where the damage sits matters more than the size of the file. A small corruption near the start of the image data can be more damaging than a larger one at the end, because decoding depends on the data that came before it.

The thumbnail as a fallback

Many HEICs carry a separate thumbnail image. When the primary picture will not decode, that thumbnail may still be intact, because it is a distinct item with its own data.

Extracting it gives you a genuine, low-resolution copy of the photograph. It is not a reconstruction and it will not print well, but it can identify the picture and preserve a record of it.

Not every file has one, so a 'none found' result is normal and does not mean the extraction failed.

What recovery cannot do

A tool cannot restore bytes that were never written or that have been overwritten. Anything claiming to repair a file with no image data left is either reconstructing something approximate or reporting success without evidence.

It also cannot tell you what the missing part of the picture looked like. Interpolation can smooth over a gap, but the result is an invention and should be described that way.

Be wary of any process that overwrites the original in exchange for a fix. If the attempt fails, you have lost the evidence as well as the picture.

Keep the original

Always work on a copy. Recovery attempts should never overwrite the only version of a file you have, because a second attempt at a partially readable file does not always behave the same way as the first.

Copy the file first, then run every attempt against the copy. If a tool writes its output in place, that is a reason for caution on anything irreplaceable.

If the photograph matters, make the copy before doing anything else, including before opening it in an unfamiliar program.

Lowering the odds next time

Most corruption is a transfer problem, so the first defence is letting transfers finish before disconnecting a card, a cable or a sync. Ejecting storage properly is tedious and it prevents a common failure.

Backups handle the rest. A file that exists in two places is not lost when one copy is damaged, and a backup taken before an edit protects you from the edit as well as from hardware failure.

When a file does fail, keep it. A damaged original can sometimes be decoded better by a future tool, and it remains evidence of what was captured even when the picture cannot be fully recovered.