For those who have outstanding features such as legs, hands, hair, teeth or feet, then there is a market for body part modelling. Hands for instance are required by photographers shooting jewellery for instance.
This is a specialised category and can be very profitable. A model may look great in a full length picture but may not have good enough feet to show on their own, This is where a girl with very good shaped feet and toes can step in (pardon the pun) who may not look so good as a full length etc.
The requirements would be for smooth blemish free skin, slim ankles or wrists, no corns, cuts, scratches etc. and well shaped neat nails.
Models are used to show shoes, jewellery, creams, sprays etc. Legs may be used to model stockings and tights. Most parts of the body can be used to advertise provided they meet the criteria required by the client.
Should you have an outstanding feature you could arrange for photographs taken specifically for use to offer to clients or other photographers.