First, make sure that the background offers a clear contrast to the seat post. For example, if the seat post is black, a white background is suitable.

It is important to hold the phone as parallel to the seat post as possible so that we can recreate the geometry of the post as accurately as possible. To get a good photo, it can be helpful to fix both the seat post and the phone. For example, the seat post could be clamped into a bike repair stand to minimize movement in the image.

Ideally, the photo shows only the bottom of the seat post, while the outer surfaces are not visible.

In addition to the photo, we need two measurements of the seat post: the depth (A) and the width (B) at the widest point. To keep tolerances as small as possible, these measurements should ideally be taken with a caliper.

In order to determine the angle of the frame to the seat post, another photo from the side is required.