Every card(ic) would be connected with a personal id card, plus security cameras. Ofcourse I can't prevent people from stealing/damaging, but they will know that they could easily be caught!

Thank you for this suggestion and your previous as well, but a suitable public space is not possible to be found in the center of my town...

Ok, but consider how you will verify the identity of whoever you issue the personal ID cards to, and they really live or are from wherever they say they are from. Not everyone captured on security tape is caught. On a related note, what insurance/liability will you offer or carry against this happening? Note again, just having a sign that says you're not liable for stolen property (ie. leave at your own risk), doesn't mean you're really not liable.

I might give them an appropriate "contract" to sign, in order to ...leave them at their own risk!

I think I will not be able to verify the intentity of every user, so the problem remains, in my opinion. In order to insure the safety of the bikes, I might change the opening hours to 8:00-24:00 and hire a person, so nobody could have access to the parking place... I loose the 24h open store, but maybe true insurance is more important!!

There are these (or variations of these) scattered around in various locations in Europe ....

Or here's what they do in Amsterdam ... this is at a train station ...

That's Rowan walking his bicycle through the middle of it all in front of me ...

She is only endorsing ideas. That politicos may read.