The ImageMagick tool lets you do almost everything you would want to with an image. You can tweak, poke, prod, and otherwise meddle with pixels (Figure 1). In this tutorial, we'll look at how to use this tool to form a command that can help protect our privacy online. This is also the perfect excuse to see how we can use the Linux terminal to build up a complex, powerful command from many smaller commands.

When you take pictures on a digital camera, a whole lot of information is stored along with the actual image. The exact information varies from camera to camera but might include things like the camera settings and location at which the picture was taken. This information is all useful until you start sharing the images online, at which point it can be used to trace exactly where you've been. Many tools will just remove the location data, but we want to be a little more clever. We want to keep the general area the picture was taken but remove the precision. We want a command that embeds the location to the nearest town. Rather than put this information in hard-to-read metadata, we want the info displayed in the image itself as a caption at the bottom. This can be done as shown in Listing 1.

Obviously, this command is a little complex, but don't worry. It's made up of lots of smaller bits that are all easy to understand. Let's break it down and look at it bit by bit. The two basic building blocks of this command are the pipe (|) and command substitution ($()). The pipe sends the output of one command to another. In some cases, we use this to send text from one command to the next; in other cases, we're sending images. Command substitution runs the command inside the brackets and inserts the text that the command outputs in the place of the dollar sign.

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