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Calibration Markersa known reference in every image

Small standardised stickers spread across the image over the skin, never over the lesion. They give the Legit.Health platform a fixed physical and colour reference, so lesion measurements stay accurate, reproducible, and comparable across visits.

The Color Multi-Marker

The marker as deployed: a white border around a black border, enclosing the colour-patch grid.The internal 5 × 5 grid holds known colour patches used to calibrate colour between visits.

Geometry and colour, from a single photo​

Because the reference travels inside the image itself, sites need no specialised photography hardware. Each marker does two things at once.

Geometric calibration

Recover true scale

The marker's fixed real-world size lets the platform measure lesion area and perimeter from one photograph, correcting for camera distance and viewing angle.

Colour calibration

Calibrate colour over time

An internal grid of known colour patches lets the platform calibrate colour against differences in lighting and white balance, so the same lesion compares reliably from one visit to the next.

What the markers enable​

The measurement methodology behind marker-based surface-area quantification is described in the peer-reviewed study published in Skin Health and Disease (2026). See the full validation and results on the surface area measurement study page.

Medela A, Sabater A, Fernández G, Mac Carthy T, Aguilar A, Herrera D, Falqués M, Martorell A. Overcoming measurement challenges in clinical practice: a deep learning-based approach to monocular surface area measurement. Skin Health and Disease. 2026. https://doi.org/10.1093/skinhd/vzag064

Supply and provisioning responsibilities​

Roles are split so that the Provider owns the marker itself and its specification, while the Customer handles distribution and logistics through its own field organisation.

  • Legit.Health (Provider): Producing the calibration markers and the print-and-cut specification
  • Customer, through its field organisation: Distributing the markers to the participating sites, and identifying which centres and site staff take part
  • Camera provider (Customer) or site staff: Calibrating each camera model used for image capture, including smartphones
  • Site staff: Placing the markers and capturing the images in-clinic, or handing them to the patient or caregiver in decentralised studies and explaining their use

The Provider supplies the markers and their print specification and trains the participating doctors. The Customer funds the engagement, identifies the participating centres, and uses its field organisation to deliver the markers to those doctors.

In this section​

The documentation splits by who needs it: the specification, the people capturing images, sites using a non-mobile camera, and the subjects being photographed.