nTools

Phone photos explained: HEIC, EXIF metadata and your privacy

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A photo from a phone is more than a grid of pixels. The file also records when it was taken, on which device, which way up the phone was held and, often, where you were standing. Most of the time that is useful: it sorts your gallery and puts pictures on a map. When the file leaves your hands, the same data travels with it.

This last part of the series looks inside the file: what a HEIC photo contains, what the EXIF metadata records, why some photos appear sideways, and how to check and remove the location before you share. We also tested what the nTools image tools keep, with a photo prepared to carry typical phone metadata.

What is inside a HEIC file

HEIC is not a single image format so much as a container. HEIF, the container, can hold several images and the data that goes with them; HEIC is a HEIF file whose pictures are compressed with HEVC, the video codec. Apple’s engineers described what an iPhone puts in it when the format was introduced in 2017:

Android can open HEIF images from Android 9, and saving them is possible from Android 10 on devices whose hardware supports it.

Converting a HEIC photo to JPEG keeps the main picture. Whether the metadata comes along depends on the converter, as the tests further down show.

What EXIF records

EXIF is a standard for photo metadata, managed jointly by the Japanese electronics and camera industry associations JEITA and CIPA. In a JPEG it sits in a small block at the start of the file. A typical phone photo records:

It takes very little space. In our test photo the whole EXIF block, including the position, was 344 bytes in a file of 436 KB.

The position is precise. Coordinates are stored in degrees, minutes and seconds, with fractions of a second; one second of latitude is about 31 metres. GPS.gov puts the accuracy of GPS-enabled smartphones at about 4.9 metres under open sky, worse near buildings and trees. That is enough to point at a single house.

Why some photos appear sideways

The camera sensor always writes the picture the same way round. When you hold the phone upright, many phones do not rotate the pixels; they store them sideways and set the EXIF orientation tag to say how the picture should be turned for display.

Browsers follow that tag by default: the CSS image-orientation property starts as from-image, which applies the EXIF orientation. Software that ignores the tag shows the photo on its side. There is a second, more lasting way to get there: removing the metadata without first rotating the pixels.

The nTools image tools avoid this: the browser turns the picture the right way up as it reads it, and the copy is saved with the pixels already upright, so it no longer needs the tag.

What the nTools tools keep

We prepared a test photo with typical phone metadata: maker and model, date and time, an orientation tag and a GPS position on a public square. Then we ran it through the tools, in Chrome, and checked the files they produced:

ToolOutputEXIF and GPSOrientation
Original test photoJPEG, 436 KBPresentTag: rotate 90°
Image resizerJPEG, 341 KBRemovedPixels upright, 1280 × 854
Image converterWebP, 318 KBRemovedPixels upright
Image converterJPEG, 366 KBRemovedPixels upright, 1280 × 854

Both tools draw the picture onto a browser canvas and save a new file from it, which copies pixels and nothing else. The HEIC converter works the same way: it decodes the HEIC into plain pixels and saves a JPEG from those, so location, dates and device details are not copied. Everything happens in your browser; the photo is not uploaded.

The flip side: the copy has no capture date either. Galleries that sort by date taken may place it on the day you converted it. Keep the original if you want that history.

HEIC to JPEG converter

Check what a photo reveals

Remove the location before sharing

Apple and Google document these steps:

Removing the metadata does not remove what is in the picture. Street names, house numbers, school uniforms, a car’s number plate or a view from a window can reveal as much as GPS coordinates. Look at the picture as a stranger would before posting it.

Frequently asked questions

Does converting HEIC to JPEG remove the location?

It depends on the converter. Some copy the EXIF into the JPEG. The nTools HEIC converter does not: the JPEG it saves has no location, date or device details.

Do social networks remove the location?

Some services remove it when they process an upload, but this varies from one service to another and is not something to count on. Email attachments and file-sharing links pass the file on exactly as it is. Remove it yourself when it matters.

Why does my photo show the wrong date after converting?

The date the photo was taken is stored in the EXIF. A copy without metadata falls back to the file’s own date, which is when the copy was made.

Why is my photo sideways in one program and fine in another?

The pixels are stored sideways and an orientation tag says how to turn them. Programs that ignore the tag show the stored pixels. Saving a copy with the nTools resizer or converter rotates the pixels themselves, so it looks right everywhere.

Does turning off location for the camera affect other apps?

On an iPhone the setting under Location Services is per app: setting Camera to Never only stops new photos from being tagged.

Is a screenshot of a photo safer to share?

A screenshot does not copy the photo’s EXIF, but it keeps everything visible in the picture, at lower quality. Removing the location from the original is usually the better option.

Previous in the series ← Image size explained: pixels, DPI, file size and quality

References

  1. Library of Congress — Exchangeable Image File Format (Exif) Family
  2. Apple Developer — High Efficiency Image File Format (WWDC17)
  3. Android Developers — Supported media formats
  4. MDN — image-orientation CSS property
  5. MDN — Window: createImageBitmap() method
  6. GPS.gov — GPS Accuracy
  7. Apple Personal Safety User Guide — Manage location metadata in Photos
  8. iPhone User Guide — Browse photos and videos by location
  9. Preview User Guide — See where a photo was taken
  10. Google Photos Help — Understand, find & edit your photos’ locations
  11. Google Photos Help — Change your camera location settings

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