Guide
Which images can be folded into a book?
One sheet of paper takes one fold, which is the whole craft in a sentence and explains every rule below. A folded book is a few hundred vertical strips of paper standing on edge — so the picture has to be something a few hundred vertical strips can say.
These fold well
A solid silhouette
One shape, filled, nothing behind it. Every sheet gets one clean fold and the outline survives at any size.
Bold lettering
Thick strokes read from across the room. Thin script does not — a hairline disappears between two folds.
An outline, if you will cut
Hollow designs keep their inner detail only with Cut & Fold, where you cut in at each edge instead of folding past it.
These never can
Each of these produces a PDF that looks perfectly normal until you have folded a hundred pages. They are worth knowing by sight.
A photo of someone's finished book
This is the most common one, and the most understandable — you saw a piece you liked. But the generator folds what it is given, and what it is given here is a picture of page edges. A vertical strip through such a photo crosses around eighty separate dark stripes; a clean silhouette crosses one.
Find the design itself, or the same subject in the pattern library.
A dark poster or photograph
Folding treats every dark pixel as ink, so a black background is not background — it is the design. The whole page block folds forward and you get a solid slab with a faint dent where the subject was.
Use a background-free version, or search the subject plus the word "silhouette".
Artwork adrift in empty space
A shape occupying the middle third of a wide picture leaves most sheets with nothing to fold. The design comes out small and pinched into the centre of the book, however many pages you give it.
Crop the empty margin away so the shape fills the frame.
The two-second test
Squint at the picture until the detail goes. If you can still tell what it is, it will fold. If it dissolves into grey, so will the finished book — folding removes far more detail than squinting does.
The generator now runs the same check for you and says so before you download, so you are never finding out after the folding.
Not sure? Start from one that works
Every pattern in the library has already been measured against these rules — the ones that could not hold their shape were not published. If the subject you want is in there, it will fold.