Probably due to metadata stored with the image regarding camera's orientation at time of capture.
You can flip it back by placing two copies of the container field on the layout with one rotated. Hide Object when or a two panel slide control could be used to control which copy of the field is visible.
FileMaker ignores the orientation in EXIF header when showing in a container.
But a web viewer or an interactive container may show it right!
in MBS Plugin we can load such image, rotate it, clear the EXIF orientation and save it so FileMaker shows it correctly.