Hay,
I got question, how you guys know that you didn't spot this car already? Is there any trick, like you save reg. plate or some thing so you can just check it before you take pictures or ... ? 
It's also a good exercise for your memory to try and remember all the license plates that you've spotted — at least the letters in the combinations, which you can easily associate with a particular model. For instance, spotter auto-moto0611 can tell you with a 99% certainty if he has ever spotted a given car or not — and he has spotted more than 5,000 so far

. I'm a bit of a license plates freak myself and I also enjoy memorizing licence plate numbers

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