The accelerometer for the iPhone is indeed an awesome addition for a handheld device but this can get quite on your nerves at times. When you are trying to show your favorite pictures to someone it often happens that while you move your phone the photo begins to flip between landscape and portrait modes. This useful tip can save you from feeling dizzy over flipping photos with constantly changing orientations.
What you need to do is select a picture in the Photos app on your iPhone in either mode. Then, tap on the picture and hold for a few seconds with your finger. You can let go once the ‘Copy’ bubble appears. Now the picture gets locked in the same orientation and any movement or rotation will not let the orientation alter. You need to tap the image again to unlock this.