Davidm wrote:

However, I have recently uploaded all the photos to my SkyDrive,
mainly as an offsite backup (I also have local backups on external
hard drives). I have noticed on SkyDrive that all (I think) of the
portrait photos are displaying as landscape. This also happens when I
upload them to a media player that I have.

There's a bit of EXIF data that specifies the orientation the photo was
taken in, but it's only relatively recently been supported all over.
That you had to rotate them in ACDSee[1] means you were using a version
that didn't understand this EXIF value (which the camera was generating
originally) so, when you rotated it, it didn't update it. Result: a
photo that's got its portrait bit set that's then been physically
rotated so when it's displayed the s/w rotates it another 90deg.

Some s/w offers the option of ignoring the rotate value which would keep
the backward compatibility.

[1] Sounds like the version I used to use. 4 or so. Got it off a cover
disc somewhere.

--
Scott