User - The user of the app has a suspicious lesion on their skin that they are curious or worried about. Their motivation to use the app is to obtain an assessment of the risk that the skin lesion might be a cancerous melanoma.
Dermatologist - A Dermatologist can use the app to help assess the risk of a skin lesion. By extracting feature data from an image the app can present a summary of the extracted data to the dermotologist.
This is the schema used to describe the use cases.