3×4 cm photos to print
3 × 4 cm (30 × 40 mm). The guide puts the head, chin to top of the hair, at about 2.4 to 2.8 cm.
9 on a 10×15 photo print, 36 on A4 and 40 on Letter.
Print the PDF at actual size (100%, not "fit to page"), or take the sheet JPG to a photo kiosk and print it as a 10×15 (4×6) photo.
No. It all happens in your browser, and the photos never leave your device.