Cropping your photos is an essential photo skill. But have you ever taken the time to learn the Crop tool's secrets? Here are five things you should know about this unassuming little tool.

1. Crop to a specific aspect ratio

Here's a trick that people typically take a long time to figure out on their own, but is absolutely revolutionary once you know about it. No matter what photo-editing program you use, odds are really high that you can tell the Crop tool to cut a rectangle in some specific aspect ratio. If you tend to click the Crop tool and then just try to eyeball an 8-by-10-inch aspect ratio, use the aspect-ratio setting to work more effectively. In Photoshop Elements, for example, click the Crop tool (tenth item from the top of the toolbar) and then choose a specific entry from the Aspect Ratio menu in the Tool Options palette at the top of the screen. To go back to a freeform crop box, select No Restriction.

2. Flip the orientation of the crop

Suppose that you are trying to make a 5-by-7-inch crop box, but all you get is a landscape-oriented crop when what you really want is a portrait orientation. You might already have figured out that you can type directly into the W and H boxes in the Tool Options palette to switch the order of the 5 and 7. But here's an easier way: Simply click the arrows between the crop dimensions, and the photo editor will flip the orientation automatically.

3. Crop to inches or pixels

Sometimes you need to crop an image to an aspect ratio based on pixels, not inches. Web designers and bloggers, for instance, often need an image that's exactly 500 by 400 pixels to fit in a particular part of a Web page—and inches, of course, don't mean much on the Web. Pulling off this trick is easy as well. You've already seen that the W and H boxes contain the aspect-ratio values, such as "7 in." and "5 in." But if you type a number and add "px" instead, your photo editor will know that you mean pixels. Keep in mind, however, that all you're doing is setting the aspect ratio of the photo, so indicating, say, 500 by 400 pixels will produce exactly the same cropping results as indicating 5 by 4 inches.

4. Cropping doesn't resize

Unfortunately, this item can be confusing, and it's related to the issue I mentioned in the previous tip. When you crop a photo to 5 by 7 inches, for example, you're not necessarily sizing the image to 5 inches by 7 inches. The same is true with pixels—a 500-by-400-pixel crop might produce a photo that's actually 1000 by 800 pixels. Why? You're cropping the photo to a specific aspect ratio, not to a particular physical size. Once you specify an aspect ratio, you can make the crop box bigger or smaller to achieve the perfect composition. If you want the image sized to a certain number of pixels, however, you need to do that in a second step. In Photoshop Elements, choose Image -> Resize -> Image Size, and specify the size you need. This step actually reduces the image to the desired number of pixels.

5. Use the Recompose Tool as a magic crop

If you own Photoshop Elements 10, you have a superpowered Crop tool hiding in the same cubby as the usual one. When you use the Recompose Tool, Photoshop Elements smartly edits the less critical elements in a photo while preserving the important details. Consider this photo of the Grand Canal in Venice, California, for example.

5 Things You Need to Know About Cropping

If you wanted to crop it into a 5-by-7 portrait photo, you might have to throw away a lot of detail on the left or right of the image. But by using the Recompose Tool, you just drag the edges of the photo in (or choose the desired crop size), and Photoshop Elements trims away some of the canal in the middle of the photo, keeping the houses and canoes intact.

5 Things You Need to Know About Cropping

[Dave Johnson is a technology journalist and author of three dozen books. He writes about photography and business technology from Seattle, Washington.]