Also known as: コギャル, 黒ギャル
Kogal (コギャル), a substyle of Gyaru (ギャル), is a Fashion trend among young female Japanese high school students.
They follow the trends of gyaru fashion in their heavy makeup (especially around the eyes), sometimes Tan skin, use of English-influenced slang (kogyarugo or コギャル語), coloured (and often bleached) hair, and trendy gyaru style fashion. Since they are school girls, they use their School Uniform as their fashion statement, often wearing their uniform skirts very short and paired with Loose Socks.
If there aren't any obvious signs of kogal (school uniform, Loose Socks, Scrunchie, etc) then it's recommended to just tag the image with the more general Gyaru.