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Never assume a photo's original framing is the best option available. The Rule of Thirds is one of photography's oldest and most trusted guides. It states that if you cut the image in thirds horizontally and vertically (making 9 mini squares), the most interesting elements should always be the lines and intersections. In Photoshop, these lines appear automatically when cropping, making it easy to improve.  Even small crops can dramatically improve a photo. Are there any unnecessary elements in the corners of the frame that you can eliminate to focus on more interesting things? Always put major lines, like the horizon in the example above, on a third line. To crop a photo, press "C" to pull up the crop tool. The Red Eye Tool is found under the Patch tool, which is found underneath the eyedropper icon in your toolbar. You can also press J to bring up the Patch tool, then click and hold on the icon to reveal the red eye tool. Once you have it, simply click and drag over the eyes to remove red eye. Want to get rid of that small pimple on your forehead? The spot healer is here to help. Click and hold the Patch tool (press "J") to find it, as it will pop up in the small menu under the Patch tool. This tool simply replaces the spot you click on with pixels surrounding it, blending them in perfectly. This means thin, small issues, like a zit or a power-line in the background, can be quickly erased without ruining the image. The healing brush works similarly, but you can tell it which pixels to replace from. To select the "healing area," hold the Alt/Opt key, click once, then start healing your blemish area. For example, imagine there was some dirt on the lens that you missed, which put a big brown spot in the sky of your beautiful landscape shot. Content-fill can cover it up for you. To do so, use Quick Selection tool (found under the Lasso icon) to select the smudge. From there:  Click "Select" → "Modify" → "Expand." Expand the selection by 5-10 pixels. Select "Edit" → "Fill." Select "Content Aware" in the Fill, dialogue box and select "okay." Imagine you've got a great shot of a soccer player in action but there is one fan in the background up against a fence that you want out of there. Of course, you need to remove him while keeping the fence, which may seem impossible when he's covering the fence up! The patch tool will take another section of the fence and duplicate it over your man to replace him.  Use a selection tool (like "Quick Selection") to select the thing you want to be removed. Select the Patch Tool by pressing J. It can also be found underneath the eyedropper icon. Click on the selected area (the place you're replacing), but don't let go of the mouse. Drag the selected area to the spot you want to replace it with and let go of the mouse.
Crop pictures using the "Rule of Thirds" as a guide for compelling shots. Use the Red Eye Tool to simply clean up the eyes of any portraits. Play with the spot healing brush to remove small blemishes. Use the Content-Fill effect to remove objects and simple imperfections. Use the patch tool to replace small sections of a photo with another section of the photo.