Tesera Studio

Privacy Policy

Last updated: 11 September 2026

Tesera Studio OÜ, a private limited company registered in Estonia at Sepapaja tn 6, 15551 Tallinn, Harju Maakond ("Tesera Studio", "we", "us"), designs and publishes mobile apps under its own brand. This policy explains what personal data we collect, why we collect it, and the rights you have under the EU General Data Protection Regulation (GDPR). For the data described here, Tesera Studio is the data controller.

This one policy covers our website at teserastudio.com and both of the iOS apps we publish: Open Signal: Cell Tower Finder ("Open Signal") and PhotoStamp (each, an "App"). Section 3 describes exactly what Open Signal does with data, and section 4 does the same for PhotoStamp; every other section applies to both.

The short version

  • We do not sell or rent your personal data.
  • Our apps do not require an account, and we do not show ads inside them.
  • Optional subscriptions are billed by Apple — we never see your payment details.
  • PhotoStamp does its work on your device: your photos and videos are never uploaded to us.
  • Our apps collect only what they need to work, plus limited usage data that is not linked to your identity, so we can improve them.
  • You can contact us at any time to exercise your privacy rights.

1. Our website

This website is largely static. You do not need an account to use it. When you visit, our hosting provider (Vercel) records standard server logs — your IP address, browser type, the page requested, and a timestamp. We rely on these logs only to keep the site secure and reliable, on the legal basis of our legitimate interest in operating a safe and stable service. Logs are retained for a short period and then deleted or anonymised. This site does not use advertising or tracking cookies.

2. Email contact

If you write to us at info@teserastudio.com, we use your message and email address solely to read and reply to you. We do not add you to any mailing list, and we keep the correspondence only for as long as needed to handle your enquiry and any reasonable follow-up.

3. Open Signal: Cell Tower Finder

Open Signal helps you see nearby cell towers and coverage and understand the mobile signal your device is receiving. To do that, the App works with the data below.

3.1 Location

The App asks for permission to access your device location. We use your location to show your position, to find cell towers and coverage near you, and to display the strength of the signal where you are. You can grant or deny this permission and change it at any time in iOS Settings; without it, location-based features will not work. When you look up towers near you, your approximate coordinates may be sent to our backend so it can return relevant results. We do not use your location to identify you, and we do not build a profile of your movements.

3.2 Cellular and network information

To do its job, the App reads technical information your device exposes about the mobile network — such as the network operator, signal strength, connection type, and cell identifiers (for example MCC, MNC, and cell ID). This is used to identify the tower you are connected to and to show you signal details. It is technical network information, not data about who you are.

3.3 Reference data from our backend

Information about cell towers and coverage is stored in our backend, which is hosted on Supabase, and the App queries it to show you results. This reference data describes towers and networks, not you. It may be derived from publicly available datasets and measurements.

3.4 Usage and diagnostic data

We collect limited, aggregated usage data to understand how features are used and to optimise the App, using the services described in section 5. This is configured so that it is not linked to your identity. The App has no account, so we do not collect your name, email address, or login credentials through it.

3.5 Purchases and subscriptions

The App offers an optional paid subscription ("Pro"). Payment is handled entirely by Apple through your App Store account — we never see or store your payment details. To unlock and restore your subscription we use RevenueCat, a subscription management service, which records your purchase history and subscription status against an anonymous, app-generated identifier. There is no account and this data is not linked to your identity; we use it only to make Pro features work and to understand overall subscription performance.

3.6 Advertising attribution (App Tracking Transparency)

We may advertise the App on the App Store using Apple Search Ads, and we want to know which campaign brought a new user to us. For that, the App shows Apple's App Tracking Transparency ("ATT") prompt asking for permission to track. The App works exactly the same whether you allow or deny. If you allow, Apple's advertising identifier (IDFA) and Apple's AdServices attribution token are used — via RevenueCat — to link your install to the ad campaign that led you to the App. If you deny, we receive only Apple's standard, non-identifying attribution. This campaign measurement is the only "tracking" the App performs, and you can change your choice at any time in iOS Settings → Privacy & Security → Tracking.

4. PhotoStamp

PhotoStamp is a camera app that prints the date, time, and place onto the photos and videos you capture and can apply film-style colour filters. The stamping itself happens entirely on your device, and your photos and videos are never uploaded to us. The App works with the data below.

4.1 Camera and microphone

The App shows a live camera preview, takes photos, and records videos so it can stamp and colour them. The microphone is used only while you record a video, so the video has sound. Camera frames and recordings are processed locally on your device and are never sent to us or to anyone else. iOS asks for your permission before the App can use the camera or microphone, and you can change either choice at any time in iOS Settings.

4.2 Photos and videos

You can also pick photos from your library to stamp. The App uses Apple's system photo picker, so it only ever receives the images you choose — it has no access to the rest of your library. Each finished photo or video is saved back to your library as a new file, using a save-only permission; the original is never changed. Nothing you capture, pick, or save is uploaded anywhere.

4.3 Location

If you add a stamp that shows where a photo or video was taken, the App asks for permission to use your device location and prints that place — as coordinates, a nearby address, or the name of a nearby spot — onto the copy. To turn coordinates into readable place names, the App uses Apple's location and Maps services, which means your approximate coordinates are sent to Apple for the lookup, under Apple's own privacy policy. The most recent result is kept only on your device so the stamp has something to show while a fresh lookup runs. Your location is never sent to Tesera Studio and never included in the usage data described in section 4.4, and we do not build any record of where you have been. If you deny location access, everything else still works — only place stamps are unavailable. Keep in mind that a date or place printed on a photo or video becomes part of the copy you save, and travels with it if you share it.

4.4 Usage and diagnostic data

We collect a small set of product events, using the services described in section 5, so we can see whether the App's flow works — for example that onboarding was viewed, that the paywall was shown or dismissed, and that a photo or video was saved. These events never include your photos or videos, your location, or the text of any stamp, IP addresses are discarded on arrival, and nothing is linked to your identity. If the App hits an error or crashes, a diagnostic report (the error, the device model, and the operating system version) is sent to us so we can fix it. The App has no account, so we do not collect your name, email address, or login credentials through it.

4.5 Purchases and subscriptions

The App offers an optional paid subscription ("Pro"). Payment is handled entirely by Apple through your App Store account — we never see or store your payment details. PhotoStamp does not currently use any third-party subscription service; if that changes, we will update this policy first.

4.6 Advertising attribution (App Tracking Transparency)

We may advertise the App on the App Store using Apple Search Ads, and we want to know which campaign brought a new user to us. For that, the App shows Apple's App Tracking Transparency ("ATT") prompt asking for permission to track. The App works exactly the same whether you allow or deny. If you allow, Apple's advertising identifier (IDFA) and Apple's AdServices attribution token may be used to link your install to the ad campaign that led you to the App. If you deny, we receive only Apple's standard, non-identifying attribution. This campaign measurement is the only "tracking" the App performs, and you can change your choice at any time in iOS Settings → Privacy & Security → Tracking.

5. Analytics and error reporting

We use two service providers to keep our apps reliable:

  • PostHog — product analytics, so we can see which features are used and where people get stuck and improve the experience. We configure it to avoid collecting information that identifies you personally.
  • Sentry — error and crash reporting, which sends us diagnostic information when something goes wrong (such as the error, the device model, and the operating system version) so we can fix it.

We do not display ads inside our apps, and neither PostHog nor Sentry is used for advertising. The only advertising-related processing we do is the Apple Search Ads campaign measurement described in sections 3.6 and 4.6, which runs only with your App Tracking Transparency consent. We never sell your personal data.

6. Legal bases for processing

Under the GDPR, we rely on the following legal bases:

  • Consent — for accessing your device location, camera, microphone, and photo library, and for advertising attribution, each of which you grant through the corresponding iOS permission prompt and can withdraw at any time in iOS Settings.
  • Legitimate interest — for keeping our website and apps secure and reliable, and for improving them through non-identifying analytics and error reports.
  • Legal obligation — where we must process data to comply with the law.

7. Who we share data with

We keep our supply chain small. We rely on the following processors and sub-processors, each acting on our behalf:

  • Vercel — website hosting and the server logs described in section 1.
  • Supabase — backend and database for Open Signal.
  • PostHog — product analytics for both apps.
  • Sentry — error and crash reporting for both apps.
  • RevenueCat — subscription management and restore for Open Signal, and the Apple Search Ads attribution described in section 3.6.
  • Apple — distributes our apps through the App Store, processes all in-app payments (we never receive your payment details), answers PhotoStamp's location and Maps lookups described in section 4.3, and, where you opt in through your Apple settings, provides us with limited, aggregated App Store analytics.

We do not share your data with anyone else except where we are legally required to do so. Some of these providers may process data outside Estonia; where that happens, we rely on appropriate safeguards such as the EU Standard Contractual Clauses.

8. Data retention

We keep personal data only for as long as it is needed for the purpose it was collected. Server logs are retained briefly and then deleted or anonymised. Analytics and error-reporting data are kept only as long as they are useful for understanding and improving our apps, and are then deleted or aggregated. Email correspondence is kept for as long as needed to handle your enquiry.

9. Children

Our website and apps are intended for a general audience and are not directed to children under 13. We do not knowingly collect personal data from children.

10. Security

We take reasonable technical and organisational measures to protect the data we handle. Where our apps or website exchange data with our servers or service providers, it travels over encrypted connections, and we limit access to the information we hold. No system is perfectly secure, but we work to keep the risk low.

11. Your rights

Under the GDPR, you may ask us at any time to:

  • confirm whether we hold personal data relating to you, and receive a copy of it;
  • correct information that is inaccurate or incomplete;
  • delete your data, or restrict how we use it;
  • object to processing that is based on our legitimate interest;
  • receive certain data in a portable format.

Because our apps have no account and we do not link usage data to your identity, there may be cases where we genuinely cannot single out the data relating to you specifically — but we will always help wherever we can. To exercise any of these rights, email info@teserastudio.com. You also have the right to lodge a complaint with the Estonian Data Protection Inspectorate (Andmekaitse Inspektsioon) or your local supervisory authority.

12. Changes

We will revise this policy as the studio and its apps evolve. The "Last updated" date at the top reflects the current version, and we will post any material changes on this page.

13. Contact

Questions about this policy? Reach us at info@teserastudio.com.