Each time you browse the web, your browser follows certain steps to ensure that information stored remotely can be seen on your screen:
If you want to save an image, you can do a save image command on your browser. But in certain cases this is not so simple, that's when catch-http can be handy.
catch-http can intercept the browser's HTTP connections and save the files that has been already downloaded into your machine using tcpflow (a great program that can record the TCP connections), and if you want to download (legally, of course. Like music with a CC license) mp3 songs, it can automatically rename the files using the IDv3 tags with libmp3-tag-perl.