Phone-camera tips for mm-perfect centering.

• 01

  Flat surface, neutral background.

  Phone camera, card on a desk, table, or dark mat. The background doesn’t matter much for the ML detector — what matters is that the card lies completely flat (no curl, no sleeve, no bend).

• 02

  Shoot straight down.

  Hold the phone parallel to the card, lens directly above the center. Tilting the camera by even 5° introduces perspective distortion that makes the centering measurement read off by 1–2%.

• 03

  Even, diffuse light.

  Avoid direct sunlight or single point sources — they create glare and shadow lines that can confuse the auto-detection. Window light bounced off a wall is ideal. Overhead room light is fine too.

• 04

  Fill the frame.

  Get the card to fill at least 70% of the photo width. More pixels per millimeter = more accurate measurement. Don’t use digital zoom — just move the phone closer.

• 05

  Tap to focus on the card.

  Most phone cameras autofocus on the closest object. Tap the screen on the card to lock focus — sharp card edges are critical for both the auto-detection and the manual handle alignment.

1. Put the card on a flat surface, dark mat preferred.
2. Phone held parallel, about 15–20cm above the card.
3. Tap the card on screen to focus.
4. Adjust until the card fills most of the frame.
5. Snap. Done.

The four most common photo mistakes that throw off centering accuracy:

• Card in a sleeve. Sleeves add 0.5–1mm of border on each side — measurement reads wider than it should. Sleeve OFF.
• Glare on the print frame. Bright reflections in the border area can shift the auto-detected edge by a few pixels.
• Bent/curled card. The bend creates a non-rectangular outline that breaks the geometric model. Flatten the card first.
• Heavy crop/digital zoom. Lower resolution = noisier edges. Always shoot at the phone’s native lens, no zoom.