Over the years, I have come across many ways to extract objects out of an image. I still use most of them mainly because each method responds to certain situations where other methods won't work. There are 7 techniques that will be explained but I'm sure there are many that I am still missing. If you know of anymore, please post a comment. I'm always looking for new ways to speed up my post-processing work.
Method 1: This technique is the simplest and is kind of a brute force way of separating and object from its background. You will notice that in the image below, the background is complicated with many colors and geometry, but the object that is being cut is simple in form. This makes Method 1 a good candidate to be used. It won't take to much time or effort to erase around the box.
1. The first thing to do is unlock the background layer so that the background can be erased. Double click in the space next to the layer name in the Layer Palette. A dialog box will come up and choose "OK".
2. Select the "Eraser" tool and make sure the brush is a small size with 100% opacity. There is an important tip that makes this method a little easier. Click on the edge of the object be cut with the eraser too. Then hold "Shift" and click somewhere else along the edge. A straight line is drawn between the two clicks. Erasing using this method is much quicker and more precise than trying to free hand erase around the object.
3. Once a path has been erased around the object, increase the size of the brush and proceed to erase the rest of the background. That's it, you are left with just the object ready to be dragged into your illustration.