If you buy a stamp with what appears to be a picture of the face of Lady Liberty on it - think again. The NY Times reports that the picture on that stamp was not taken at the Statue of Liberty in New York harbor. Instead, it was taken in Las Vegas at the New York - New York Casino. Sharp-eyed stamp collectors noticed the difference.
How did the USPS make this mistake? Photographs are for sale online from image brokers like Corbis, iStock, Getty, and many others. To help purchasers find the image they want, most of these brokers attach some form of metadata to the image. The ability to find a particular image is directly related to the kind of metadata attached to the image. The metadata describes the image. Since you can't search an image itself you must rely on the words associated with that image, that is, the metadata.
Think of cataloging as the ultimate form of metadata. Being able to use the words associated with ("attached to") a book, a periodical, or a looseleaf to search for that item helps the researcher find it in the collection being searched. Some collections are huge. Without the ability to search the metadata even the best researcher could not find exactly what is in a collection. This is why the catalog is such a useful tool when you are doing any research including legal research. Without the catalog you miss materials that are out there for you to find or you won't be able to find the exact item you are looking for.
And, it is the metadata in the catalog that keeps you from making a bonehead mistake like the one the Postal Service made. If the image that they chose had been correctly identified and cataloged in the first place they wouldn't have picked a picture of a half size ripoff of a national icon to put on their stamp.