Sometimes images are presented rotated through metadata, rather than actually rotating the image. Check the metadata on the original to see if it includes this. Then open an issue on lemmy's github project, if there isn't one already.

Or maybe it's just its way of telling you that you should be taking pictures like that in landscape orientation.

Same problem here: https://lemmy.ml/post/1172803

I thought it was because of the orientation of the pic, but I posted another one later with the same orientation, and it was correct. I wonder what causes this.

I was expecting the screenshot to also be rotated, but it's not. Huh.

This was me using Connect.