Labs · 🟢 Local sample verified · 1 November 2026 · Viewer and cleaner compared
Slack image lab: what did the local files contain before any Slack download?
Before I drop a JPEG into Slack, is GPS still in it, and does a local clean remove those fields?
Local JPEG reads found GPS in the source and no GPS keys after a clean. One October file was 24,407 bytes. Those reads are not a Slack download of the same file. Clean the copy in this browser before sending. The file stays on this device and is not uploaded to this site.
| Field | Local JPEG | Platform download not run |
|---|---|---|
| Bytes | 24,407 | Platform download not run |
| Pixels | 1200 by 800 | Platform download not run |
| GPS | 35 deg 0' 0.00" N, 135 deg 0' 0.00" E | Platform download not run |
| Make / model | CPK Fixture / Local JPEG | Platform download not run |
| DateTimeOriginal | 2026:10:29 09:00:00 | Platform download not run |
WhatsApp Help: media and documents; WhatsApp Help: longer videos
The October file was 24,407 bytes with GPS near 35°N, 135°E. A mat2 copy of that file had no GPS keys. The November viewer pass is the homepage cleaner comparison on the later sample.
Short answer
Direct answer: local reads found GPS in the sample and no GPS in the cleaned or mat2 copy. That is not a Slack download.
- What was measured: The 29 October JPEG and the 1 November viewer sample both carried GPS in the source file. Cleaned copies omitted those keys.
- What that does not prove: A file Slack might store is a different object. This page does not describe it.
- What you can do first: Clean the copy in this browser before the file leaves the device. Nothing is uploaded to this site.
🟢 Local sample verified · 1 November 2026 · Viewer and cleaner compared
- Published
- Last updated
- Last tested
What we measured
Sample dated 2026-11-01. The viewer read location and camera fields. The cleaned file no longer has them. The file stayed on this device.
| Field | Local sample (viewer) | Cleaned copy (cleaner) |
|---|---|---|
| GPS / location | 35 deg 0' 0.00" N, 135 deg 0' 0.00" E | No GPS |
| EXIF | EXIF present (camera make, model, and settings) | EXIF fields cleared |
| Camera information | Camera make and model present | Camera make and model removed |
| Timestamps | 2026:11:01 18:00:00 | Capture time removed |
| Provenance / C2PA | JUMBF APP11 and a C2PA container | No C2PA or JUMBF container |
| Recompression / resize | 378,066 bytes, with location and the metadata above | 361,097 bytes; metadata removed, image scans unchanged |
GPS / location
The viewer read 35 deg 0' 0.00" N, 135 deg 0' 0.00" E. The cleaned file had no GPS.
EXIF
The viewer read a camera make, a model, and the capture time 2026:11:01 18:00:00. The cleaned file had no EXIF.
Test environment
Chrome 156.0.8078.47 and ExifTool 12.76. The file stayed on this device. Nothing was uploaded.
How to test your own file
- Upload as image and as a file if both exist.
- Download from another account.
- Compare.
Methodology
Every published result has to follow the same protocol: a known source file, a recorded hash, a specific upload path, and a downloaded copy. Folklore does not count.
Privacy implications
Treat internal Slack as a sharing surface. Strip location and device tags before dropping a photo into a channel.
The file before you upload it
On 29 October 2026 Pillow 10.2.0 drew a 1200 by 800 JPEG and ExifTool 12.76 wrote a GPS position of 35 deg 0' 0.00" N, 135 deg 0' 0.00" E. The file is a fixture, not a camera photo of a person. It was not uploaded to Slack. The delivered-copy column above stays “Platform download not run” for that reason.
| Field | Local JPEG | mat2 0.13.4 copy |
|---|---|---|
| Bytes | 24,407 | 28,220 |
| Pixels | 1200 by 800 | 1200 by 800 |
| SHA-256 | 898c1d7d2e423ebe2211551f9d8311f52af9ca997539449b1319f79aa400d326 | f995aa073fc361c388e75a13efcdc67cd81230fffe20f4177d333fa551305557 |
| GPS | 35 deg 0' 0.00" N, 135 deg 0' 0.00" E | No GPS keys |
| Make / model | CPK Fixture / Local JPEG | Absent |
| DateTimeOriginal | 2026:10:29 09:00:00 | Absent |
mat2 source.jpg wrote the second file. ExifTool listed no GPS keys on it. Make, Model, and DateTimeOriginal were absent. The byte count went from 24,407 to 28,220. Width and height stayed 1200 by 800.
What Slack Help said the same day
Add files to Slack returned HTTP 200 on 29 October 2026. Members and guests can add files up to 1 GB. The desktop composer accepts up to 10 files at once. An image preview displays inline only when the longest side is under 25,000 pixels and the image is under 45 million pixels total. The article does not say whether an EXIF GPS IFD is still in the file a teammate downloads.
Read the fixture, or your own file, in the Image Metadata Viewer before you drop it in a channel. The same JPEG is written up on the WhatsApp HD note, which also has no upload result.