Implement a filter for transforming background images

[jfroelich]

Several articles use a strange technique to display a foreground image. Perhaps it is to prevent simple copying of the image (basically to disable right click) or it has something to do with responsive design or progressive loading of assets. Basically, the image is specified as a background image using CSS for an element, and then the element or a child of it is sized so as to occupy the desired space.

For a specific/narrow set of the cases where this happens, I can rewrite the dom by removing the background image from the css, and adding a new child image element.

This will help out in several other cases. For example, telemetry and boilerplate analysis.