Privacy Policy

Last updated: July 28, 2026
Changelog: Fully revised now that the training-data upload feature is live (first published: July 27, 2026)

1. Overview of What We Collect

We send data to our server only when you explicitly choose to do so on the "Training Data" screen. Outside of that action, the app never sends anything externally.

What gets sent:

• The captured photo itself (only for items you choose to send)
• Detected tile positions and predicted classes
• The hand you confirmed (omitted if not confirmed)
• Capture timestamp, model version, and app version
• An anonymous, device-generated upload ID and capture session ID

What never gets sent:

• Your name, email address, phone number, or contact information
• Location data (any location data embedded in a photo's EXIF is removed on-device before the photo is even stored)
• Advertising identifiers or device identifiers (the upload ID is a random value generated by this app alone and is not shared with other apps or services)
• Usage analytics

2. Camera Use

The app uses the camera to read mahjong tiles.

• All image analysis runs entirely on your device
• Photos are sent only when you explicitly choose to send them on the "Training Data" screen described below
• Camera access requires your consent through the iOS permission dialog; if you decline, the manual tile entry features remain fully available

3. Data Stored on Your Device

Only if you explicitly enable the save setting on the "Training Data" screen will captured photos and recognition results be stored on your device.

• This setting is disabled by default
• EXIF data (such as location) is stripped from the photo on-device at the moment it is saved
• Stored data stays on your device and is not sent automatically
• It is excluded from iCloud backup
• You can delete it at any time from the same screen, individually or all at once
• It is removed when you delete the app

4. The Upload Feature

To improve recognition accuracy, we use data you contribute to train the tile recognition model. Because training a tile detector requires the images themselves, this feature transmits the captured photos. The bounding box coordinates alone cannot be used for training.

We commit to the following:

• Transmission happens only through explicit user action; nothing is sent automatically
• Before sending, you can review exactly what will be sent for each item individually and choose which ones to include
• A confirmation dialog is shown at the moment of sending

Photos of a mahjong table may capture the hands or surroundings of other players present. Please take this into account when deciding whether to contribute.

5. Storage Location and Retention

Uploaded data is stored using object storage (R2) provided by Cloudflare, Inc. The storage location may be outside Japan.

We do not use authentication; data is managed solely by the anonymous upload ID generated on your device. It cannot be linked to your name, email, or other identity.

Uploaded data is retained until the developer incorporates it into the training dataset (typically within one to three months of upload), at which point it is annotated and prepared for training. We do not currently publish the dataset itself to third parties; if that changes, this policy will be revised accordingly.

6. Revoking a Submission

You can revoke previously uploaded data from the "Training Data" screen. There is no authentication mechanism, but knowledge of the upload ID (a device-generated random value) is treated as authorization to delete the data associated with it.

The "Training Data" screen displays the first few characters of your upload ID. Even after deleting the app, if you have this string you can request deletion by contacting us via GitHub (@ktakada42).

That said, we may be unable to honor a deletion request in the following cases:

• If the app was deleted or reinstalled and the upload ID was lost, so that even you can no longer identify which data was sent
• If the data has already been incorporated into and annotated as part of the training dataset
• Once a model has finished training, it is not technically possible to remove the contribution of any single piece of data from its weights

7. Third-Party Sharing

Uploaded data is stored with Cloudflare, Inc. (R2) as described above. We do not share data with any other third party.

8. Analytics and Advertising

The app uses no analytics tools and no advertising services.

9. Children's Privacy

The app does not collect personal information such as your name or contact details, regardless of your age.

10. Changes to This Policy

Any changes to this policy will be published on this page.

11. Contact

For questions about this policy, please contact us via GitHub (@ktakada42).