I'm a marketer and wish to enable a tracking mechanism on my clients' websites so that both they and I have data demonstrating the effectiveness of the ads. These ads are real-world ads, like billboards.
I know it's fairly easy to set up a facebook pixel or a google analytics tracking on any website. However, this data would be client owned, and not accessible by me. So how do I create my own "pixel" and use it to track the effectiveness of a particular campaign which uses a very specific landing page?