That's the part the article explains.
But the hypothetical artist would have to understand what he was atempting to paint on glass... adjusting his paint opacity inversely to distance from shroud surface and using the glass's transparency in place of dark paint shadow. This is NOT an intuitive thing to do. Wilson's artist knew what he was attempting to accomplish.
The "photograph" that Wilson produced with his technique is exactly that: a photo-graph - a picture written with light. The image on the shroud shows NO light artifacting... shadows, etc. Its artificiality is very apparent in the mesa like appearance of the 3D effect because the gradient of the paint opacity is artificial.
I am willing to bet that Wilson's sun-bleached photographs will disappear quite rapidly with time and exposure to light because the unbleached linen that comprises his image will bleach out.
To "duplicate" the shroud's image, the proposed example has to meet many criteria to be deemed successful... Wilson's contender meets only two of about 20 requirements.