If you've turned your camera to switch from landscape view (horizontal) to portrait view (vertical), you may need to rotate the image in iPhoto to view it right side up.
Ways to rotate photos:
In organize or edit mode, to rotate one or more photos clockwise, select them and click the Rotate button (Figure 4.14 and Figure 4.15). To rotate the selected photos counter-clockwise, hold down and click the Rotate button.
Figure 4.14. Here I'm showing a "before" photo in the display pane and in its own window just so you can see both Rotate buttons.
Figure 4.15. Here's the "after" picture that resulted from clicking the Rotate button.
In organize or edit mode, select one or more photos, -click one, and choose the desired rotation direction from the contextual menu that appears.
In organize, edit, or slideshow mode (but not book mode), select one or more photos and choose either Rotate Clockwise () or Rotate Counter Clockwise () from the Photos menu.
You can change the direction used by the Rotate buttons in iPhoto's Preferences window; -clicking always reverses the default direction (Figure 4.16). How you set it is purely personal preference based on how you tend to rotated your camera for portrait-orientation pictures.
Figure 4.16. In the Preferences window, select which direction you want iPhoto to rotate photos by default.
It may be easiest to rotate photos in batches in organize mode. Shrink the thumbnail size so you can see a number of photos at once, -click the ones that need rotating clockwise, and click Rotate. Repeat with any images that need counter-clockwise rotation, holding down when you click Rotate.
Some cameras automatically rotate the image, eliminating the need for Rotate.
iPhoto 6 creates copies of rotated photos in the Modified folder rather than rotating just the thumbnail, as some previous versions did.
If you rotate a GIF image, iPhoto converts the image to a JPEG, which may be undesirable.