Point the rear camera at the grass or into a bush. The model runs entirely on this phone; nothing is uploaded.
First run downloads a 12 MB model. Tap Start and allow camera access.
Collecting training photos: tap the ball on screen — the frame is saved with that spot marked. Use Save frame (no tap) for scenes with no ball or with look-alikes.
For distant balls: turn on Far mode in Settings and use the zoom slider — each doubling of zoom doubles the range.
Works best in daylight. At dusk, use the Torch button (Android) — a lit ball stands out far more than the grass.