Sea turtles belong to the superfamily Chelonioidea and inhabit all of the world's oceans except the Arctic. There are seven species of sea turtles.
Chelonia mydas or green turtle
Eretmochelys imbricata or hawksbill turtle
Natator depressus or flatback Turtle
Caretta caretta or Loggerhead Sea Turtle
Lepidochelys kempii or Kemp's Ridley turtle
Lepidochelys olivacea or Olive Ridley turtle
Dermochelys coriacea or leatherback turtle
The above Image shows how to identify species of a sea turtle based on its carapace or the back. Anyone with idea of Graph theory would immediately recognize the graphs drawn on the carapace of different turtle species. I believe this is a good criterion for automated species identification from sea turtle photographs.