Lighting first
Light matters more than camera quality. Soft daylight from the side or front usually works better than a bright overhead light. If the center of the palm is shadowed, line detail becomes harder to interpret.
Avoid flash glare, heavy filters, and warm color casts that hide fine creases.
Framing the hand
Keep the palm centered and include the wrist base plus fingertips. The hand should be relaxed, not stretched painfully flat. A natural open palm gives enough line detail without distorting the shape.
If the app supports retaking the photo, compare the preview before submitting.
When to retake
Retake the image if the palm lines look smudged, if the edge of the palm is cut off, or if shadows cover the area below the fingers. A better photo usually creates a more specific report.