The US passport and visa size
2 × 2 inches (51 × 51 mm), head 25 to 35 mm from chin to crown, plain white background, no glasses. The guide follows them.
Yes. Download the single photo, a square 600 dpi JPG. Resize image and Compress image fit it to pixel or KB limits.
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.