Check out illusions knitting. Taking yarn and making a hidden message.
Check out Donna’s book Kitty Knits for a scarf that was included in the book that is similar.
Illusion knitting relies on the fact that ridges of garter stitch and ridges of stocking stitch in knitting have different properties. Garter stitch ridges stand forward further than stocking stitch and this allows you to create a design that changes its appearance dependent on the angle of viewing. In illusion knitting two colours of yarn are used to create alternate ridges of knitting, a dark coloured ridge followed by a light coloured ridge. Areas of dark or light can be brought into the foreground, when the piece is viewed at an angle, by using garter stitch for that particular part of a ridge and stocking stitch for that portion of the preceding ridge. When the piece is viewed from directly in front only stripes of colour should be seen. Our maths and my maths/art background allowed us to develop the charting process for this technique to the point where I can create far more complex images than have previously been possible, incorporating not just areas of dark and light but also areas of various levels of intermediate shading. Check out more here.
Here is the scarf from the Kitty Knits book.