Rotating selection in Preview (see thread 'How can I rotate the text box in Preview')
No answer required, as I'm elaborating on a solution: When attempting to rotate a rectangular image selection an arbitrary number of degrees, I had success only after pasting the selection in a different document, then using the two-fingered technique mentioned in the 'How can I rotate the text box in Preview' thread (note I did NOT have to hold down ⌘ as others did). If you attempt to rotate an entire document in this manner (no selection), it will rotate in 90 degree increments. Using High Sierra on 2012 MacBook Air. Hope this helps somebody.