The metric implemented in the Image::Density Perl Module estimates the density of data where there is data, and has a reasonable correlation with goodness as judged by humans. That is, if you let a human look at a set of images and judge quality, the density values for those images as calculated here tend to correlate well with the human judgement (densities that are too high or too low represent "bad'' images). It is intended for use on bitonal TIFF images, such as those from scanning paper documents.
ucview is a video image capture application that uses the unicap toolkit. It provides a simple way to parametrize the video device, can capture still images from the video stream, or record the stream as an MPEG file. By using unicap, it can access many different video capture devices like webcams, video grabber boards, IEEE-1394 (FireWire) cameras, and others.