Manual:$wgEnableAutoRotation/en

Usage
To explicitly disable image auto-rotation, add to the bottom of LocalSettings.php:

Explicitly setting to true is probably a bad idea (since if the image renderer supports rotation, it should be auto-detected).

Details
If it is true, MediaWiki will look at the EXIF Orientation metadata field (which is set mainly by smartphones and some cameras, when pictures are taken sideways) and automatically rotate the image to the correct orientation.

If not set in LocalSettings.php (or if set to null) then this setting takes its value from BitmapHandler::canRotate method - which returns true if the image rendering method supports rotation.