We currently don't map the numbers 1 through 8 to any meaningful value.
However, showing the text by specification ("top, left") like Gwenview does is also not very helpful.
Instead, show an icon and transform it accordingly.

All possible orientations according to http://sylvana.net/jpegcrop/exif_orientation.html

In Dolphin sidebar:
(took a vertical photo:)

same for "Details" tab (larger font size leads to larger icon, hence non-filled look)

One issue is that dynamic coloring doesn't work, so in e.g. Dolphin's tooltip the icon remains black