In Octoprint i can rotate image stream form my usb camera, i tried doing it in MJPG-Streamer on my other raspberry and it doesn't work.
Do you mind sharing your tricks?
The rotation inside OctoPrint is managed inside the webcam and timelapse settings and is done within the web interface itself using CSS transforms if I'm not mistaken. This means, that a pure mjpgstreamer pi wouldn't necessarily do the same thing. I think there might be command line options you can use to do it inside mjpgstreamer as well. This article might shed some light into your situation.