• Exif Orientation Page
• EXIF orientation handling is a ghetto – Dave Perrett (page dates from 2012, so some of the web apps which didn’t handle well EXIF data may have improved. But you get the picture)
• KeyJ: Why Your Photos Don’t Always Appear Correctly Rotated
• The most evil feature ever conceived: the Exif Orientation Tag (also 2012)
• HowtoGeek Chris Hoffman Why Your Photos Don’t Always Appear Correctly Rotated

(Drawing by Calvin Hass, published on his page: JPEG Rotation and EXIF Orientation)

Solution: exiftran.

To autorotate all jpeg files in the current directory:
exiftran -ai *.jpeg