Can't rotate photos imported from a flash card  

Though it's now a few weeks after the original post, I'll state this anyway, in case it's of benefit to someone: Windows Photo Viewer is not a good way to rotate photos. If either the height or the width of the picture being rotated are not exactly divisible by 8, Windows Photo Viewer will re-save the pic in jpg format, meaning you lose picture quality, since jpg is a lossy format. Windows Photo Viewer will warn you the first time that you do this on a Windows installation. If you tick the "In the future, do not show this dialog" checkbox, you'll never see the warning again, and would probably soon have forgotten that it still applies.



Even if your camera's pics all have heights and widths divisible by 8 [for all the pic sizes selectable in the camera's settings], if you crop and save a pic, whether that pic be from your camera or downloaded from the internet, the saved pic might not have height and width cleanly divisible by 8. So you would lose picture definition if you rotated it.

The preferred solution for many of us is to simply never use Windows Photo Viewer to rotate pics. But if it's the default picfile viewer, it's easy to accidentally click the rotate buttons. So we install a third party freeware program of choice as the default photo viewer. I use Irfanview, which has a Jpg Lossless Rotation feature. Irfanview has both lossless and lossy rotation options, and all programs have a learning curve, so if you adopt this solution be sure to properly study the program help. If you use Irfanview, be sure to download and run the plugins installer after running the main program installer. Also study the program's lossless rotation options, as some of them can remove picture file metadata you'd probably prefer to keep, if not set the way you want.

These webpages describe some of the issues I've mentioned:
https://www.raymond.cc/blog/rotating-photos-or-pictures-in-windows-photo-viewer-causes-quality-loss
http://www.betterjpeg.com/lossless-rotation.htm

This Wikipedia table mentions 'JPEG lossless rotate' in the 'Other functions' column for those programs that are capable of it:
https://en.wikipedia.org/wiki/Compar..._and_licensing

Happy rotating!