1. Correcting a tilted horizon

Unlike some of the easier-to-use photo editing programs such as Paint Shop Pro or PhotoImapct, Adobe Photoshop doesn't have any handy little gadgets to automatically straighten tilted horizons or leaning buildings, but it can still be done. The method is a bit long-winded but not that difficult. It's also a useful technique for freely rotating a layer when compositing several images together.

Step 2.

Convert your image into a layer by double-clicking on its bar in the Layers palette, then click OK on the dialogue box that appears.

Step 3.

Activate the rulers with the keyboard shortcut CTRL+R. Using the Move tool (top right on the tools palette) click and drag on the rulers bordering the image, to drag out guide lines that will help you judge horizontal and vertical correctly. Drag one from the left and one from the top, and position them near easily identifiable lines in the picture, such as the horizon or a vertical wall.

Step 4.

Go to the Edit menu and select Free Transform. A box with drag handles will appear around the layer containing your image.

Step 5.

Move the mouse cursor near to the corner of the image, but just outside it, and you'll see the cursor turn into a tool for rotation. Carefully click and drag to rotate the image until the straight lines match up with the guides.

Step 6.

Delete the blue guide lines either by dragging them back to the edges of the image, or by selecting Clear Guides in the View menu. This step isn't strictly necessary, because these line will not saved as part of the final image anyway, but it looks neater and anyway a good workman always tidies up afterwards.

Step 7.

Finally crop the image to remove the exposed background, then flatten the layer by selecting Flatten Image in the Layers menu. Save the corrected image under a different filename if you want to keep the original version intact.