I recently put some old photos on my zenphoto site. Although they all displayed OK in Photoshop, when zenphoto displayed them some were rotated through 90 degrees - the old digital camera didn't record the angle at which the photo was taken. I have now rotated all of the pictures, and while the main photo for each now displays correctly the thumbnails are still sideways. How can I force zenphoto to reload/recreate the thumbnails?

You can delete the cache folder or at least the images you want to be created new within your zenphoto installation manually.

The Pre-cache Images link on the Admin Overview page will clear the cache (delete all the files) and then force a reload of all images. This is probably overkill if you have only a few images. Then acrylian's suggestion to delete the images from the cache is best.

Right, I forgot that the pre-cache-link does that too...