Print at 100% / actual size, with “fit to page” disabled. The complete artwork must measure 80 mm wide for a 30 mm duck. Use matte paper.
50 mm — check with a ruler after printing
Scan with your phone to open the AR camera directly in Safari or Chrome. Allow camera access, then aim at the whole card again. If shared through WhatsApp, send the PNG as a document to preserve detail. A second screen works for a trial; its display size determines the duck’s apparent size.