Why does it matter if the ad is visible? When those same companies post in People magazine, they pay for the placement they want and get no data about how many people saw the ad.
The agencies that buy the ad verify it was placed in the right spot at the right size and that's about all they can do.
Why should the web be any different? As long as they insist on bundling javascript with their ad, I'm going to run an ad-blocker.
What? Because it can - it's the biggest reason so much money is transferring to digital and away from print, because of data and accountability. An ad that was at least scrolled into view is better than one that isnt and many campaigns are now bought on that basis.
It's not perfect but it's far better than before and we're not going back.
CPG can't be tracked is the problem, there's a major last mile / offline attribution issue and it's only getting tougher as security/privacy gets more regulated.
That being said, we work with P&G, they definitely know more now than decades before with older mediums.
Because this is running on the customer's browser, CPU efficiency doesn't matter at all. They can do all sorts of stupid things, like grab the DOM from the browser, lay it out in a JS rendering engine and see if their div ends up being visible.
I haven't had the time to look through the ad javascripts on your typical fat webpage, but when there's tens of megabytes of code and it pegs my CPU at 100%, I know it's doing more than just displaying a .png in an iframe.
Could you just pick a couple of pixels from the actual page display and check they're the right color?
Not sure either of these work without access at the top page level, ie you can't get the data from scripts in an iframe? Been a while since i did any JS dev.
While people have done that, most ads seem to load load with some JS to confirm if the ad is visible, and if it's above or below the fold.