The Ruler Tool
The Ruler tool is an often overlooked tool hidden beneath the eyedropper on the Photoshop toolbar. You can use it to to measure lengths, straighten photographs and place objects exact distances apart. In short, it’s very handy. Here’s a video showing you how to quickly straighten a lopsided photo.
How to Straighten A Photograph With The Ruler Tool in Photoshop (Notes)
1. With your photograph open in Photoshop, select the Ruler tool.
The Ruler tool is hidden under the Eyedropper tool in the toolbar. Press and hold, or right-click on the Eyedropper to reveal the hidden tools, then select the Ruler tool.
2. Click, then drag along the edge of something in the photograph that should be perfectly vertical or horizontal.
2. Click the Straighten button in the Options bar. If you’ve made a mistake when drawing a line with the Ruler, hit the Clear button instead of Straighten and start over.
3. To crop away the areas that have become transparent, select the Crop tool, and use the handles to drag an area that encompasses the part of the photo you want. Then hit Enter/Return on the keyboard or press the Commit button on the Options bar.
You should now have a nicely straightened and cropped photo.