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https://ico.org.uk/your-data-matters/domestic-cctv-systems-guidance-for-people-using-cctv/
If you are capturing images beyond your property boundary
Which a typical video doorbell facing the street will and many standalone cameras too
Let people know you are using CCTV by putting up signs saying that recording is taking place, and why.
Never seen that next to a video doorbell or domestic CCTV.
There are other requirements too, hard to tell if they are being met by walking down the street.
Purposely filming people outside your house for no other reason wouldn't cut it.
But happening to record things that go on outside your own property when the main purpose is for security is likely to be covered as a legitimate basis for doing so, as long as you don't hang on to the footage for longer than necessary.
Caveat Reddit but: https://www.reddit.com/r/gdpr/comments/g93yq1/how_does_gdpr_affect_public_filmingpictures/
My neighbours security cameras caught a dawn raid by 40+ riot police over the road from us. Not going to post that...