I often recognise that people blur their license plates on pictures on the internet in Germany. I can't figure out what's the fuss. The information is public nevertheless (I mean it's on your vehicle), nobody but appropriated authorities can get any data out of it, and people also do it on platforms where they are identifiable anyways (Facebook, car selling platforms etc.).
So what's the problem of having your license plate visible on the internet (in Germany/EU)?
It records where someone was, and you don't know what that reveals about someone.
This part is discussed in a lot of comments and answers. An overview:
You drive around with it all day, so it gets lots of exposure already. However, that doesn't mean that even more exposure is desirable. Aganju's answer explains:
posting on the internet opens that information to a much larger number of people everywhere in the world, not just locals that care to look. [...] Also, on the internet, it's shared forever.
And O. R. Mapper comments on another answer:
the information that someone owns a given car with a given license plate is arguably "public" [but] the information that this car (and thus, probably, its owner) was at a specific location at a specific time may be a very different story.
Alright, so the internet has a higher chance of containing someone who can use the data to harm you, than if you limit the exposure to those around you... but what evil things could someone do with something that is already so public?
Lots of people can think of an answer to this:
It creates permanent records of things that are otherwise fleeting. You might also consider that it is costly to be everywhere in the world and record movements of a large amount of people, but it is very cheap to collect this data from your armchair.
These reasons might not apply everywhere in the world, or to every individual, but are you sure it does not apply to each of the license plates in your picture? They did not ask you to share it, so why do you need to do it? It's their data, they have a right to choose what happens to it. Which brings us to the legal aspect.
In case your picture contains (a) license plate(s) that are not of your car, it may not be legal to share this online.
I can only speak for the European Union, where we had privacy guidelines since 1994 (Data Protection Directive, implemented as laws by many countries) and legislation since 2016 (General Data Protection Regulation). Privacy is part of the European Convention on Human Rights.
The definition of personally identifiable information (PII) according to the DPD is (paraphrased): any information about a person who can be identified, directly or indirectly, in particular by reference to an identification number or to one or more factors specific to his physical, physiological, mental, economic, cultural or social identity. GDPR slightly broadens this:
any information [identifying a person], directly or indirectly, in particular by reference to an identifier such as a name, an identification number, location data, an online identifier or to one or more factors specific to the physical, physiological, genetic, mental, economic, cultural or social identity of that natural person.
So it does not matter that I cannot trace that NL 12-ABC-89 belongs to Jan de Vries, it matters that there exists an entity which can do this. Therefore it is PII. This means you need a reason to process the data, which can be:
Alright, but you just took a picture of good weather on your business trip, and a car happened to drive by. Can you really not show your wife? Yes, under GDPR you can. Wikipedia cites:
The regulation does not apply to the processing of data by a person for a "purely personal or household activity and thus with no connection to a professional or commercial activity."
It's a matter of privacy.
The thing you definitely determine from the license plate in some countries is the county of the registered car. In small countries some counties have a small number of registered vehicles and that eases tracking one.
Other things you may be able to determine in quite a lot of EU countries:
year of birth of the owner (since some use 2 number character in the plate number)
name of the owner (since many use the 2 or specially 3-letter abbreviation of their name)
Example: a car in Romania with the number CT-90-GEO will give you quite good information: the location of the registration is in the Constanta county (abbreviated CT for vehicles) and the owner is named George and was born in 1990.
So many people prefer not to release something like this in the wild.
CT gives you certain information. 'Overmind' must have meant that the owner can pay to customize the other letters/digits if they don't want to just be assigned a combination. This answer was phrased in a somewhat misleading way and some of the commenters assumed that the code is always assigned based on name/birthday by the government. It is not the case.
It is to protect the privacy of the individuals.
Imagine that you can link the license plate of a car to the owner. You take a picture of a car in Berlin and share it in the internet, you will be giving this information to all persons on the internet that the car was sighted in Berlin and thus violating the privacy of the owner that might not wish no one knew he was in Berlin. European laws protect the individual rights.
You can take the pictures but you cannot share them publicly without protecting the faces or information that can break someone else privacy.
In the UK people often obscure licence plates in photographs they post online to protect themselves or the vehicle's registered keeper (often the owner) from "number plate cloning".
Number plate cloning is where someone acquires licence plates by having them produced without providing proper documentation (1). This is usually done in order to steal the registered keeper's identity, making it harder to attribute criminal activity committed in a vehicle to the actual perpetrator (2).
Posting pictures of your licence plate online makes it easier for criminals to find licence plates to clone, especially when attempting to match the make and model of another vehicle they are in possession of (3). Cloning the plate of a vehicle with the same appearance (make, model, colour, body type) means that everything will appear in order if a cursory check of the plate is carried out.
Since the license plate is (indirectly) linked to a person, it can be used to identify a person. As such, it is "personal data" as defined by the GDPR. It is now illegal to share such data without prior authorization from the car owner. Because its location at a specific time can be deduced (near the car, at the time of the picture), it is an even more sensitive information.
However, in EU people did not wait for the GDPR to blur license plates in order to protect the privacy of their owner. Even though the registry of license plates is not public, it is easy for stalkers or jealous wife/husband/whatever to remember a few license plates and recognize them when they encounter them by chance. People generally do not want to be involved in an argument between ex-lovers, especially when it can be in front of a court (divorce judgment, etc).
Only half an answer:
People are not always logical about their choices of personal information sharing.
They like to have their initials and their birth year on the license plate, and show off those vanity plates, but at the same time they don't want their initials or their birth year known in the internet, and give fake birth years or initials when signing up somewhere.
It might be because posting on the internet opens that information to a much larger number of people everywhere in the world, not just locals that care to look. Or simply the feeling that you 'know' the audience that has access, like sharing your birthday or your home address with all members of a local chess club (even though you don't really know them all). The whole world out there for sure contains some bad people, and nobody has even remotely the feeling that he knows the whole world, so people are quite reluctant to share anything personal in public.
Also, on the internet, it's shared forever. You can change your number plate next year, and after a while, no neighbor or colleague might remember your old one; on the internet, it stays always accessible.
In a nutshell, it is psychologically motivated.
TLDR: Europeans are privacy aware and don't share what they don't have to share; there is a practical difference between something being public locally and globally
To approach this a bit more broadly and from a cultural perspective:
Europeans are often more aware of privacy issues than say Americans:
With respect to protecting information that is public anyway:
It's not about the number, it's about the time & place.
Most pictures store a place (GPS coordinates) and a timestamp today, or would allow a placement based on the image content.
Posted images could suggest where a specific person was at the time of taking of the picture.
Because of the of the internet is so easy to gain people's information. The last thing you want is someone tracking you down because they like the way your vehicle looks, or they want the stereo out of it, or they like the way the girl next door looks, or something of that nature. So most of the time it is done for privacy issues.
In the US it's common practice to blur license plates. This is another basic difference between N.America and elsewhere. In the US because of state's rights, each state has their own laws regarding plates. In Michigan, where I live, the plate goes with the owner.. You can transfer a plate from a car you sold, to a new car. And we are required to just have a rear plate, renewed each year by putting a color coded year tab over the previous years. That gives away the registered owners birth month. Our plates are valid from birth month to birth month. In California, unless it's changed recently, the plates stay with the car for the life of the car, from owner to owner. And they are required to have plates both front and back. We can get vanity plates for an extra charge, but generally plates that need to be purchased are in numerical order when delivered to the office. But with three to 15 lines at the Sec. of State office, and over a hundred offices throughout the state, you can say plate numbers are random. Each state has their own rules, so available personal info could be easier in one state than another. I never gave the blurred license plate thing a second thought. Other than high traffic video, at a longer distance, all plates are commonly blurred. It's too easy to get the info on a person if you know the plate number. With privacy, comes people who want to exploit that.
Between the information that is given out within certain counties licensing authorities, and with the online live access to many public roads and highways, cloud processing, and machine learning. For instance in America (not sure about EU and UK) with the roundabouts and tollways and tollbooths, traffic cam cctv footage, not to mention any other purposely set private cameras and manual methods. A sole hacker could quite easily find you, discover your route (more information), ID your work location, your schedule, your patterns within a matter of days, and work you with the limitless minute details that add up to a useful amount of info and data that is powerful. Once found they could go even further by simply querying and crosschecking public information to fully Identify you through methods that provide so much more than just a name or birthday. It's exploitable like none other. Not to mention just the limited information one could gather is valuable to dark people and businesses. I didn't know that, I'm just talking through a few small ways that if someone wanted to get info on the "rude guy that cut me at bagel n bagel" they have enough to go off and perform a full blown exploitation, or data collection operation on thousands of citizens similarly to government surveillance in the past via CCTV (not satellite), not trying to say thats what the gov does, but I hope you understand what I mean by that. I would try personalized plates, covers, and if you suspect you're being targeting which is most likely not the case as you probably would never even know if a hacker was going to come after your information to do, sell, further exploit you, or launch targeted "exploits" and hacks to get what they want or are looking for. Most likely your license plate is in more than just the governments database if you live in a highly populated city.
Id like to say don't sweat it, and you probably shouldn't if you're worried about the risks and potential but I understand why one would want to do that in areas that give you plates based on personal information.
Also consider this, covering it may draw additional attention instead of blending in with the herd. It tells exploiters you have a license plate with personal info. Either way you could get screwed so just drive my EuroBrex-friends across the pond. Even if it's not public, hackers with resources and will can ALWAYS hack or exploit you, and as long as demand exists corporations will always seek out information to exploit you through consumerist marketing ploys.
It's not 2000 anymore. Private lives are forever gone, nothing's private anyone and we've allowed that to happen due to technology and insidious governments in the name of "security" and more. The internet and tech sector are building products from realtime visual recognition and on. It's not new by any means. "Bobbies" and Police have been using it for many years to scans plates on the road, not to mention federal departments and institutions with security have been using it far longer, practically a millennial lifetime. One doesn't need to name their passwords P@ssword1 or lose a wallet, or give them your information to get hacked by an exploit these days. All it takes is the collection of information and analysis, or rather patterns in general everyday life and provided information volunteered on the web is sufficient. I'd limit it.
A simple explanation is the owner doesn't want to associate his car to themselves.
I know of some "YouTube influencers" who got their car vandalized because some haters figured out the car parked in the street was owned by that person.
If you blur the tag nobody can know who's the car owner.
The answer is simple...
Most people have little understanding of how security works or what aspects of their privacy should be protected. They see others masking the licence plate number and do the same, without serious understanding of the reasons behind such policies.
