3D images have captivated me since I was a kid. A frequent source of amusement was the "Victorian wallpaper effect" and even without a viewer I could easily see classic stereo photo pairs in 3D. Not at all difficult to see the "hidden" objects in the article's quite nice illustrations.

While popularity of SIS imagery isn't what it was a few decades ago, programmer interest in the subject has remained quite strong.

As an artist I enjoy incorporating SIS images in my work. In the past I've used a number of open-source SIS generators. Mostly these programs weren't completely satisfactory. A common defect was producing SIS artifacts marring output image appearance.

Subsequently I wrote a SIS program (with GUI for usability) [0] that almost entirely eliminated artifacts in the finished images. Developed with artists' interests in mind, its SIS output looks different vs. examples in the article. (Using depthmap and texture/pattern image inputs, the latter determines the "surface" appearance of the SIS.) However both SIS styles have the same 3D effect capability.

[0] https://thinairarts.com/stereogram.html