We all take crooked photos occasionally and if you aren't careful with the camera and hold it exactly horizontal, the resulting slope of the landscape can ruin a good photograph. This is most obvious where the horizon is horizontal, such as when you take a photo at the beach and you can see the sea, or a large lake. It is obviously crooked when the water slopes to one side of the image. Windows 8 Photos app can solve the problem and it is quite straightforward.
Open the Photos app from the Windows 8 Start screen.It shows the photos in the Pictures folder and you can browse the folders and images, and then select the one you want to correct.
It is opened for viewing at first, rather than editing, but if you click anywhere on the screen a panel opens at the bottom that contains several buttons. Click the Edit button in the bottom right corner.
The editing screen has left and right panels containing buttons. On the left are categories of functions and on the right are individual functions. Click Basic Fixes on the left and Straighten on the right. You can see that the horizon in this photo slopes a bit and the right side is higher than the left. The Straighten tool will be used to fix it.
Click and hold the mouse on the Straighten tool on the right. A grid is drawn on top of the image to help you straighten it, then you can rotate it by tiny amounts by clicking and dragging the control around the circle. Here the photo has been rotated by three degrees. Let go when it is correct.
The horizon is now straight and the photo can be saved. Click on the screen to display the bottom panel and there is a Cancel button, Save a copy, and Update original. It is always best to save a copy and you should never overwrite originals unless you have a backup elsewhere. It's not that anything will go wrong, but one day you might want the original to do some different editing.
That's it. You can now straighten all your crooked photos. Sometimes just a tiny bit of straightening can make all the difference.