Computerphile vid about steganography
The video covers jpeg steganography where data is meant to be hidden in an image by changing the least significant bit or values in the discrete cosine transform used to compress to jpeg. the idea is to have the image not be perceptibly altered and still contain as much information as possible.
From the article you mention, instead of hiding the alterations they make to the images, their goal is to have easily perceptible changes that are cyclic, and to our eyes average to what we expect from the rest of the frame.
I'd imagine you get a camera that can shoot above 120Hz and look for big jumps in chrominance in adjacent frames.
chrominance is going to be the color information from the image as opposed to the intensity.
changes in intensity are more easily detected so would probably be a less likely to be used for this.
It may be able to see if just slowed down.
and i guess instead of looking at jumps in chrominance better would be to just subtract adjacent frames into a new series of images and then just look for the frames with much less black than the other ones.