Some photos don’t really help us out… they have no horizon to make sure the photos is straight. In this particular photo (below), it was rather difficult. The water level, which I’ve come to rely on, is not straight. Looking to the left of the image, the water edge is progressively farther away in the scene. Since I took the photo about ten feet above the water, I also can’t trust the water’s edge.
I can’t trust the tree line either because it’s evidently not straight.
When I can’t trust horizontal lines, I look for vertical lines. I know this is tricky since most lens suffer from some distortion that might lead us to trust vertical lines that aren’t truly vertical. Furthermore, should the wide angle lens be tilted upward or downward, vertical lines on the side of the frame are no longer vertical.
When something is reflected in the water, I know that the reflection is perfectly aligned with it the object. Using the level tool in Lightroom’s Crop & Straighten tool, I can then align the photo vertically. Lightroom detects if you are using the straighten tool vertically or horizontally.
Simply select the level tool and find something that is perfectly vertical. Extend the line across and farther away on each side. Note that it helps not have the mouse pointer in the way.
In some situations, your photo may look better if it’s not perfectly straight. Most of the time though, making sure that the photo is straight is the best way to represent the scene that you had in front of you. For me, nothing is more distracting than a tilted photo.