Getting Rid of Dust Spots
Dust spots are a problem inherent in digital photography with cameras that use interchangeable lenses. If the dust can get in there, sooner or later some of it will end up on your sensor, and when it does, it will end up on your images. Thankfully, Photoshop provides some useful tools to get rid of spots on your images.
The best way to get rid of dust spots on your digital images of course is to not get them there in the first place. Keeping your camera and lenses (and your camera bag) clean will go a long way towards avoiding the problem entirely. A self cleaning sensor such as what Nikon built into the new D300 that shakes the sensor's low-pass filter to knock loose at least some of the dust that may be stuck to it can also help. And when you see spots, it's time to clean your sensor. But still, you can end up with spots on your images occasionally, often at the worst possible time. Learning how to fix things in Photoshop is a skill worth knowing.
There are basically four options for getting rid of spots in current versions of Photoshop: the Clone Stamp tool, the Healing Brush, the Spot Healing Brush, and the Patch tool. And if you are a Photoshop Elements user, all four can be found there as well.
The Clone Stamp tool copies one part of your image and lets you paint it to another part of the same image. You can control the size and other properties of the brush just as you would a regular Photoshop brush. This lets you feather the edges as needed to blend your changes into the underlying image. To use it, you need to pick a part of your image that is similar to the area you are trying to fix. Try to get reasonably close that that your repairs will look right. When you find what you are after, hold down the Alt/Option key and click with the Clone Stamp. Now release the Alt/Option key and click where the dust spot is.
The Healing Brush works similarly to the Clone Stamp except that Adobe has given it some smarts. While it still copies from one part of your image to another, it attempts to blend the copied pixels in by matching the surrounding texture and lighting for you. It isn't always successful, but often it is. The procedure for selecting your source and then pasting the results is the same so once you learn to use the Clone Stamp, you should be right at home with the Healing Brush.
The Spot Healing Brush takes things one step further by attempting to select the source for you. Texture and lighting are still blended for you as well. Pretty much all you have to do is click on the dust spots to make them go away. Unfortunately, in my experience, this works best with relatively simple images and often disappoints when working on real world images.
Rather than aiming for greater simplicity as the Spot Healing Brush does, the Patch tool takes things in the other direction and provides for greater control. The basic concept of selecting source and destination are still the same, but the mechanics are different. First, use the Patch tool just as you would the Lasso tool to draw around the dust spot or area to be patched. Then make sure the "Source" option is selected in the Patch tool options bar. Then click on the area you have selected and drag it around your image to find a good match for the patch source. As you drag, the area to be patched will show a preview of the results based on the pixels currently under your cursor. Keep dragging until you are happy with what you see and then release the mouse. The image data from where your mouse is will be blended into the patch area using the surrounding lighting and texture as a guide. With a small enough area to be patched and enough surrounding choices to drag to when picking a source, you can fix most any dust spot. The Patch tool isn't as quick to use as some of the other options, but it can do an excellent job when the alternatives don't seem to be working.
One confusing aspect of the Patch tool is the selection of "Source" in the options bar. The alternative choice is "Destination" and it's not entirely intuitive as to just what this choice refers to. When you first open the Patch tool, you can select "Source" or "Destination" then, but it refers not to the area you select but rather to the meaning of what you drag to. You can lasso around your selection either before or after picking "Source" as you wish. It only matters that "Source" is picked before dragging. If you pick "Destination" instead and then drag, you will be picking up your selected area and moving it around the screen as you drag to find a good destination — not what you want. If this happens to you by mistake or through confusion as to which choice to pick, just use Undo or the History palette to get things back the way they were. Remember, it's "Source" that you want.
With any of these tools, to get the best fix you can, pick the smallest brush size or selection that you can. Don't get impatient and try to cover too big an area at a time. With a bit of patience together with a bit of practice, you can fix most any spot.