Photoshop Tip: Straighten images with the Ruler tool
Tips & Tutorials, by Mark White
November 14, 2012
Here’s an easy way to quickly straighten out wonky horizons in Photoshop CS5 and CS6
If you’re using CS5 or CS6 use the Ruler tool to draw a line across a part of your image that’s meant to be level, and then hit the Straighten Layer button in the Options bar.