Often I end up taking a photograph where the horizon is not parallel to the edge. Here’s a quick way to align the horizon with the edge.

  • Select the measure tool.
  • Draw a straight line (using the measure tool) along the horizon.
  • Go to Image | Rotate Canvas | Arbitrary…. The Angle is already filled up with the right value. Do OK.
  • Now crop to your liking.

You can use this technique to straighten anything, not just the horizon.