Photo-identification is a technique used into identify and track individuals of a wild animal study population over time. It relies on capturing photographs of distinctive characteristics such as skin patterns and scars from the animal. In cetaceans, the dorsal fin

Dorsal fin

A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...

 area and tail flukes are commonly used.

Photo-identification is generally used as an alternative to other, invasive methods of tagging that require attaching a device to each individual. The technique enables precise counting, rather than rough estimation, of the number of animals in a population. It also allows researchers to perform longitudinal studies

Longitudinal study

A longitudinal study is a correlational research study that involves repeated observations of the same variables over long periods of time — often many decades. It is a type of observational study. Longitudinal studies are often used in psychology to study developmental trends across the...

 of individuals over many years, yielding data about the lifecycle, lifespan, migration patterns, and social relationships of the animals.

Species that are studied using photo-identification techniques include:

• Killer whales
• Humpback whale
  Humpback Whale
  The humpback whale is a species of baleen whale. One of the larger rorqual species, adults range in length from and weigh approximately . The humpback has a distinctive body shape, with unusually long pectoral fins and a knobbly head. It is an acrobatic animal, often breaching and slapping the...
  
  s
• Whale sharks
• Manta rays
• Octopuses (Wunderpus photogenicus)