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Feels like it's your camera performing auto-rotation on the file or setting one of the EXIF flags incorrectly.
There are 8 rotations on an image, basically 4 x 90' rotations and the 2 x flips... EXIF describes this, your camera puts that info in the EXIF. This is normalised during upload, but if the EXIF is incorrect then the incorrect rotation and flip may be applied.
Mobile cameras largely get this right, so I'm surprised that yours hasn't.
And I have no idea why the photos are uploading sideways. @velocio?