lrcat - Adobe Lightroom Files
File Juicer will extract previews from Lightroom data files. The Catalog files does not contain images so you are likely interested in the lrdata files instead. This can be a way to recover partially form a situation with missing photos where the originals have been deleted by accident.
Drop the lrdata file onto File Jucier and let it extract the images inside.
Users of Aperture and end in a similar situation where you need to extract pictures from approject files.
The lrcat files contain information about the images, and it is stored in sqlite database format which File Juicer will extract as text. Diggin into what it means is an entirely different story.