You start with a regular pattern, such as vertical lines. Then, you shift parts of the pattern in the shape of the words you want to “encode.” Click on the image below to see an easy to read example.
The hidden letters or pattern are much more difficult to see in the “message” Flyss found, because the background is so uneven. It looks to be a partly mashed radiator, probably a ’70s era air conditioning radiator for a building of between 1500 to 3000 square feet. Also, the shifted segments aren’t English letters, which makes it harder for English readers.
Here’s my attempt to trace the edges of the shifted part. I’m more sure of the horizontals than the verticals.
It looks like Japanese, I think. — Strattera