Katharina presented our P3F user study at the Usable Security (USEC) Workshop at NDSS 2017

After our first P3F concepts and prototypes, we decided to get feedback in a user study. We conducted at different places in Vienna and offered the participants three (hypothetical) picture privacy systems that have been proposed. The study was finally accepted at USEC 2017 and presented in San Diego. The study was a major reason why we shifted towards a more interactive system (as in our app solution).

See our paper for further details:

Exploring Design Directions for Wearable Privacy
Katharina Krombholz, Adrian Dabrowski, Matthew Smith, and Edgar Weippl
In Proceedings of USEC Mini Conference 2017 co-located with NDSS Symposium 2017.
[ pre-print PDF ] [ BibTex ]


P3F (Picture Privacy Policy Framework) started as a passive way of informing a photographer about oneself wishes on usage restriction on pictures. This concept bridged the analogue gap by unobtrusively encoding the privacy policy into the pattern of the wardrobe. However, we also explored active solutions based on user studies. Finally, our mobile phone based project graduated into a real app. We are proud to launch SnapShh…!, (Snapshot + Shhh!) our privacy mediator solution.

How does it work?

While professionals know, that they need to get permission from each pictured person, even considerate private people often do not have the possibilities to ask all people incl. bystanders for permission. Our app automates this process.


Everyone having this app installed will receive small thumbnails potentially containing him/herself and is asked about their opinion. The system works in the most privacy preserving fashion: It does not use GPS (just direct peer discovery based on WiFi Direct), it does not report back anything to a central server (it communicates Peer-to-Peer using GCM), it does not require any login or user account (not even a Google account), and thumbnails sent are of such low quality that there is hardly any useful purpose other than identifying him/herself.

Notifications are shown on screen and on smart watches. You can agree or disprove on a picture without leaving the current app. If too much picture are arriving in a short period of time, the app stops nagging you and you can use the picture list to review the photographs at any later time. The picture list shows your photos (right) with the current results from the other users, and your received thumbnails from other users in your vicinity. White entries need your attention (e.g., they not answered yet). You can change your opinion at a later time, and they will override your previous vote.


We don’t believe in compulsory DRM (Digital Rights Management). History has shown, that this simply does not work. Even a screenshot would circumvent this.

We believe, if we give a photographer the right tools for an informed decision he or she will think twice before uploading a photo to social network that someone is opposing.

The App is currently available for Android 4.0+ upwards. We are still investigating if we can perform a similar background vicinity detection on iOS as well.

The source code can be found in our Download-Section. To install the app, visit the Google Play Store.

New app to appear soon for Android – call for public beta

We are proud to start a limited beta of our new App that also features a new concept for our picture privacy project.

The new concept features a real-time central-server-free communication between the photographer and a depicted person. We implemented this system as an alternative to the computational heavyweight picture recognition system, after realizing that the vast majority of pictures in social networks are made by smart phones and after user studies shown that most users wish for an situational case-by-case solution for their pictures. Our system so far only produced a generic policy that had to be changed by changing wardrobe.

The new system works as follows:

An app on the smartphone of the photographer sends an small thumbnail to people in vicinity of the taken picture to ask if the receiver is depicted here and if she or he consents with a possible publication of the picture. A photographed person receives an notification on his/her phone or smart watch and is able to send an response to the photographer.

This communication is done in the least privacy invading method generally available on such phones and smart watches: We facilitate WiFi-direct – a method for building ad-hoc networks – and Google Cloud Messaging. (No, Bluetooth does not work without pairing first.)

If you wish to participate in the beta program, please write us at p3f@sba-research.org. We will start sending out invitations in about two weeks. The beta app will have an additional logging module included for allowing us to measure the performance and possible problems with the app.  This logging is not included in the final version.

Requirements: Android 4.2 or higher. If you have multiple device for testing, that’s even better.


A robots.txt for your face

The Daycon 9 “Hiding from Robots” presentation went exceptionally well. I also talked a little bit about our upcoming software we will present here on the blog shortly. The discussion was very fruitful and provided me with interesting details about the views on privacy in the States and some fresh ideas.

Daycon9 Dabrowski Presentation (PDF)


Let’s face it: Most countries have privacy laws to protect the citizen’s rights on his own image – but they are ineffective and unenforceable. Even the most careful photographer might not have the chance to ask all bystanders and unintentionally imaged people for their consent. The reality is, that almost no amateur photographer cares, and most professional photographer lives in constant fears of lawsuits. Maybe it is time to create a machine-readable privacy policy for everyone: a robots.txt for your own appearance, bridging the analogue gap between the pictured individual and the photographer. A method that would allow anyone who cares to know what permissions you gave for photographs of you. And court proof arguments for anyone who did not care.


P3F at Future Innovators Summit – developing the POST-CITY Kit at Ars Electronica Festival 2015

Adrian Dabrowski will be part of the Future Innovators Summit at the Ars Electronica Festival in Linz. This “Future Catalyst Program for the Development of the POST CITY Kit” will bring together entrepreneurs, activists, artists, technicians, and scientists from all around the world. The conclave (or workshop) is split into 3 different groups, that will discuss issues of life in future cities.

P3F clearly covers socio-technical privacy problems, that will intensify with the increasing population density. We look forward to get inspired and inspire other attendees.

The event runs from Thursday Sept 3rd to Sunday Sept 6th 2015. The final presentations will be held on Sunday 3:30pm at the conference square in the “POST CITY” next to the Linz central railway station. In the last years, most Ars Electronica Festival exhibitions were free (Hauptplatz, Kunstuni, Street installations,…) or required only a low entrance fee (e.g. OK Centre, ARS Electronica Building). If you just visit for a single day, there is no need to buy a full festival pass. You will not run out of free/cheap attractions.

Hope to see you there.

How to print your own P3F Privacy T-Shirt (Step-by-Step)

If you want to use P3F to communicate and enforce your personal picture privacy preference, all you need is a privacy T-shirt with a privacy pattern of your choice. In this tutorial, we will teach you how to create your own privacy T-shirt in a few easy steps.

The first thing you need to get started is a plain T-shirt (without any prints or clothing patterns on it; 90%-100% cotton preferred for heat resistance) in the colour of your choice. Additionally, you need to download your desired privacy pattern from here (PDF). There are three ways of getting the pattern on your T-shirt: you can either use a transfer film and print the pattern with an inkjet printer on the film and then fuse the pattern on your T-shirt. You can also upload the privacy pattern of your choice to on-demand T-shirt printing services, such as spreadshirt.de. Many copyshops also offer such services.
The P3F project team tried out the flex film transfer method by themselves: we went to Metalab and used their T-shirt printing equipment.  In this tutorial, we will explain to you how we did that so that you can do the same.

The Metalab is an open hacker space in the city of Vienna. In most cities you can find such awesome places where you can go to learn more things, exchange your knowledge and work on your own creative projects such as making your own privacy T-shirts. Most T-shirt printing and copy shops use the same technique as described below.

At the Metalab in Vienna, they have a vinyl-plotting machine (Roland GX-24) which you can use to cut out the colour film and a heat press to stick the film on the T-Shirt. Various colored films are available directly at Metalab for a small contribution towards expenses (you can also bring your own if you want to). These colour films come on a transparent carrier that hold the shapes in place.

T-Shirt Printing Recipe

1. Select a T-Shirt and (flex or flock) film colour. Consider that P3F requires a certain contrast in order to function. Therefore, we recommend colour combinations with a high contrast such as black on yellow, pink on dark blue, dark blue or black on light blue or light green on black.

IMG_20150415_1737092. Turn on the heat press so that it can pre-heat while you cut the film. Set to 170°C.

3. Place the film in the cutter, the film has two sides, a (mostly transparent) supportive layer and a sticky layer. Make sure to have the sticky layer on the upper side.

4. Open Corel Draw and load the pattern templates of your choice and convert the pattern elements to curves in order to avoid distortions and artifacts. TIP: add some extra cuts into the removed areas, to ease the peeling later on. Never put extra cuts into the colour areas.


5. Click the Icon “Cut Studio” on the menu bar. If you print text on a T-shirt you first need to mirror the motive (Object > Mirror). In case of our privacy patterns, this is not needed as they are all symmetric but highly recommended for text.
6. You also need to transfer the width of the film to the machine driver. This can be done by clicking File > Cutting Setup > Properties > Get from machine.

7. Now you should see the Graphic and the real size of the motives relative to the film. Do a final checkup before you are ready to cut. Click File > Cutting… > OK to actually cut.

8. After cutting, carefully remove the parts of the film that you do not want to have on the T-shirt. Use a sharp knife or tweezers. Usually there are no problems peeling the unused colour film from the carrier film.

9. Check the heat press, the temperature on the display should be around 160-180°C.
10. Put the T-Shirt into the heat press so that the side you want to print on faces you. Try to sleek the fabric to remove tucks and crinkles.

11. Put the film with the motive onto the T-shirt and compress it for about 20 seconds. Wait for a few more seconds so that it cools down a little.

12. Then, peel off the supportive carrier layer and compress it again for 3-5 seconds.

13. Take your privacy T-Shirt out and enjoy your picture privacy


TIP: If you have large consecutive areas of colour film removed, add some extra cuts to ease the peeling step.

PRO TIP: You can use almost any form of the polka dots (we used star and heart), as long as it has a big area filled with these dots.

Washing instructions: Wash inside-out at 40°C. Dry hanging, or use tumble dry at low temperature only.  If you like to iron, do it inside out.

If you have any questions, please visit p3f.at or contact us.

the P3F Project Team,
Adrian & Katharina