Earlier quoted context omitted.
They could add the detection to GIMP. But then that would reveal what the algorithm is. And that would allow specific strategies for producing false negatives or false positives. I'm still undecided about whether countermeasures to reverse engineering like this are useful or not in the long run.
These measures can stop a kid from counterfeiting. That's all they do. I'm sure in the process they could create some kind of sporadic troubles to designers which paid for the expensive software. You can't possibly think that a criminal organization, with average tech resources, will have a hard time getting around this in a way or another.
But that's the whole point. If you can stop the idiots from copying notes, you have a lot fewer potential counterfeiters to deal with.