On iOS the camera can be accessed before unlocking the phone, and wouldn’t this effectively put illegal image(s) in the targets possession without their knowledge?
But OK, let's say that you've found a way to get the photos and you're comfortable with the criminal implications of that. At that point why don't you just hide the printed photos in your coworker's desk? My point is that if you have a disgruntled coworker who's willing to resort to heinous crimes in order to screw you over, there's many different things they could do that are less convoluted.
If someone wanted to generate a false positive image, they could already leverage it on these other platforms.
Google Photos (+ Google Drive I guess ?) is on by default only on Pixel phone I think, and not by default on Samsung phones. For Facebook you have to post the images, for Microsoft I don't think there is any scanning inside Windows itself and by default, I guess it's on OneDrive ? Those companies are big, but the majority of pictures still go through iOS first and foremost.
To stay on the topic of iCloud, my point is that it seems quite hard to protect yourself/device from even this most basic attack scenario.