To update this thread dashcams have been ruled illegal in:-
GERMANY, AUSTRIA,SPAIN,BELGIUM,LUXENBOURG,PORTUGAL.
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This information is incorrect, at least when it comes to dashcams in Belgium. Feel free to check the information (available in Dutch and French) at
www.privacycommission.be, search for dashcams. I'll provide a roughly translated version of the current law here :
Individual use : An individual is allowed to use a dashcam to record his travels, and if he downloads this data to his PC and/or views the video himself or with his family, the rules and regulations of the privacy laws in Belgium do not apply. If however the information is shared with others (for instance posted on the internet), the privacy law comes into effect and it's rules and regulations have to be followed, which amongst other things requires the dashcam to be registered with the privacy commission.
Use of a dashcam for proof of accident/incident : In this case we are no longer considering the data gathered to be personal information, but legal personal information. Processing this legal personal information is forbidden by default, although some loopholes exist, where one is that you are entitled to process this data if it concerns yourself as an involved party, and if all other regulations regarding the privacy law are followed. One of these regulations is the fact that old data has to be erased (looping your cam can do that), data has to be kept secure, involved parties have to be informed about the fact that the incident is/was recorded by the dashcam (which would mean you have to tell the other party as soon as you can) and - of course - the dashcam has to be registered.
In short : you can use a dashcam as long as you : "don't share the data", and "if you want to use it as "proof" for certain claims, you'll have to jump through quite a few extra hoops to stay legit when it comes to Belgian Privacy Law".
More information in detail available at
http://www.privacycommission.be/nl/dashcams (in dutch). The above translation should not be considered legal or binding advice and is based on information available at the time of this post.