Before uploading a file
Check filenames, metadata, contents, redaction, upload accounts, service display, archive files, and public copies before uploading files.
Before uploading a file, check not only its contents, but also the surrounding information about the file.
Images, PDFs, Office documents, videos, audio, and archive files may retain creators, capture dates and times, location information, edit history, comments, and filenames.
After upload, the recipient can save, share, and analyze it.
That is why checking before upload is important.
Check the filename
The filename is the first thing to check.
Filenames often contain real names, dates, places, case names, school names, and company names.
| Filename example | Risk |
|---|---|
| Contains a real name | Creator or person is identified |
| Contains a date | Activity time or capture period is known |
| Contains a place | Usual places or the scene are known |
| Contains a company name | Affiliation or case is known |
| Serial number | The existence of multiple files is inferred |
The filename may be visible to the recipient as-is.
Check metadata
Metadata is information attached to a file.
Even if it does not appear visually, it may remain inside the file.
| File type | Information to check |
|---|---|
| Image | GPS, shooting date and time, camera model |
| Creator, creation software, annotations | |
| Office document | Change history, comments, organization name |
| Video | Shooting date and time, location, audio, device information |
| Audio | Recording environment, background sound, creation information |
Detailed methods for checking metadata are covered in another article.
Here, the important point is not to judge by appearance alone.
Check the contents too
Even if you remove metadata, it is dangerous if information remains in the file contents.
Photo backgrounds, PDF text, video audio, Office document comments, and folder names in archive files. This kind of information remains in a form that can be seen.
| File | What to look for in the contents |
|---|---|
| Photo | Faces, backgrounds, reflections, signs, name tags |
| Video | Voices, notification sounds, movement routes, surrounding conversations |
| Body text, annotations, redaction handling, embedded images | |
| Office document | Comments, change history, hidden sheets |
| Archive file | Internal folder names, unnecessary files, work-in-progress data |
Check both the metadata and the contents of the file.
Do not rely too much on redaction or blur
Before uploading a file, also check redaction and blur processing.
Even if information looks hidden, text inside a PDF may remain, layers from before image editing may remain, or original information may appear in thumbnails or previews.
| Processing | Caution |
|---|---|
| PDF redaction | If text is only covered from above, it may still be copyable |
| Image blur | Weak blur may allow text or faces to be restored or inferred |
| Cropping | The original image may remain in another layer or history |
| Screenshot editing | Notifications, times, and account names often remain at the edges |
| Thumbnail | Information may remain in a small image generated separately from the main file |
For the public copy, open it in another app or another environment and check that the information you want to hide is neither visible nor extractable. If you upload a check file to an external conversion service or online viewer, the file and logs may remain on that service side. If possible, check in a local environment or a trusted environment.
Check the destination and account
Also check the upload destination.
Real-name cloud accounts, workplace accounts, personal social media, visibility settings, and shared-link permissions are involved.
| Check item | Reason |
|---|---|
| Upload account | Check whether a real name or workplace information appears |
| Sharing scope | Check whether unintended people can see it |
| Owner display | Check whether the other person can see your name or email |
| Viewing history | Check whether it records who opened it |
| Edit permission | Check whether the recipient can change it |
Even if the file itself has been checked, identity may appear from the upload destination.
Check how it appears on the service
How the uploaded file appears to the recipient also matters.
Cloud services may display the owner name, updater, profile image, shared folder name, viewers, and comment section.
| Displayed information | Risk |
|---|---|
| Owner name | A real name or workplace account is visible |
| Profile image | A face or personal account appears |
| Updater | It is clear who edited it |
| Folder name | Case name, organization name, or activity name is visible |
| Comment section | People involved or internal conversations remain |
If possible, check the screen visible to the recipient from another environment or another account.
Even if it looks safe on your screen, a name may appear on the recipient's screen.
Create a public copy
Separate the original file from the public file.
The original file may need evidentiary value or work history. The public file, on the other hand, should not retain unnecessary information.
| File | Handling |
|---|---|
| Original file | Store in a safe place if needed |
| Check copy | Examine metadata and contents |
| Public copy | Remove unnecessary information before uploading |
It is safer to avoid uploading the original file directly.
Inspect every part of archive files
Archive files such as ZIP files are a format where oversights are common.
Information can come from filenames, folder names, unnecessary work files, hidden files, old versions, thumbnails, and settings files inside the archive.
| Information inside an archive file | Risk |
|---|---|
| Folder name | Real name, case name, or organization name remains |
| Work-in-progress file | Information or comments from before deletion remain |
| Hidden file | OS or editing environment information may be included |
| Old version | Personal information from before correction remains |
| Unnecessary image | Background or location information is included |
Do not check only after compressing it; organize the folder structure before compression.
Put only the necessary files into a new folder and recreate it as the public version.
Check after upload too
Checking is also necessary after upload.
Check whether the visibility is as intended, whether thumbnails reveal information, and whether previews show annotations or owner names.
| Check item | Reason |
|---|---|
| Visibility | Check whether anyone can see it |
| Preview | Check whether text or annotations are too visible |
| Thumbnail | Check whether faces, backgrounds, or documents are shown small |
| Shared link | Check the impact if it is forwarded |
| Deletion method | Check whether you can stop it if a problem appears |
Uploading does not end the moment you place the file somewhere.
Check how it appears to the recipient.
Do not upload files you are unsure about
You cannot check the metadata, you do not know how the sharing destination displays it, you do not know how to delete it, or there is legal risk.
In such cases, it is better not to rush the upload.
For anonymity, what matters more than whether you can delete something after publication is whether you can stop before publication. Once a file is shared, the recipient can save, forward, and analyze it.
There are situations where the most realistic countermeasure is not to send it while you still cannot judge.
Summary
Before uploading a file, check the filename, metadata, upload destination, and sharing settings.
Images, PDFs, Office documents, videos, and audio can each retain information that is hard to see.
If you upload from a real-name cloud or workplace account, identity may appear from the account rather than the file.
Separate the original file from the public copy, and check again before publication.
Related tools
ExifTool
An external resource related to this article. Open it only when it fits your situation and threat model.
Why it is listed: It can help with the article topic, but it is outside Anonymity Sense and should be checked before use.
URL : https://exiftool.org/
MAT2
An external resource related to this article. Open it only when it fits your situation and threat model.
Why it is listed: It can help with the article topic, but it is outside Anonymity Sense and should be checked before use.