Endless Slideshow Screensaver offers several ways to rotate your photos in a slideshow, both automatic and manual. By default, your photos will be automatically rotated using the information from the EXIF metadata. If you do not want the software to do it - open the screensaver setting, select the [ Viewer ] tab, [ Picture rotation ] section, and clear the [ Rotate pictures using EXIF data ] box:
When this option is on, the photo is automatically rotated 90 degrees left or right depending on the actual EXIF data. If this option is off or rotation did not happen as expected you can rotate all currently shown photos manually using the [ Rotate the currently shown files 90 degrees left ] or the [ Rotate the currently shown files 90 degrees right ] action. More information about the slideshow actions can be found in the Slideshow navigation and other actions article.
Another way to rotate your photos in a slideshow is using the [ Rotate pictures to a random angle ] option. If you check this box and set the degrees value (3 to 20), then every photo in the slideshow will be rotated to a random angle from 0 to the value specified in the [ degrees ] field.
The [ Overlap rotated pictures ] option is there to let you choose how the rotated photos are resized to fit the available space. If this option is off, then the pictures rotated to a small random angle are shrunk to fit the available space precisely. This will ensure that every pixel of the rotated photo is visible, but may potentially leave large areas of the screen empty especially if there is more than one photo is shown at the same time.
If the [ Overlap rotated pictures ] box is checked, the Endless Slideshow Screensaver will use more space for the shrunk pictures than is available and place the rotated photo in the center of that space. This will hide some portions of the picture outside the screen or underneath other pictures (potentially up to the value specified in the [ % of picture size ] field) but will leave less free screen space.