Shorpy credits the original photographer, if known, on the individual photos. I prefer that because it has led me to look for more works by the photographers. It's not obvious, but at the bottom right of the page, it does give general credit and a link to the LOC:

About the Photos
Our holdings include hundreds of glass and film negatives/transparencies that we've scanned ourselves; in addition, many other photos on this site were extracted from reference images [[high-resolution tiffs) in the Library of Congress research archive. [[To query the database click here.) They are adjusted, restored and reworked by your webmaster in accordance with his aesthetic sensibilities before being downsized and turned into the jpegs you see here.

The last link shows the process used on the photos. Since I'm more interested in the content than what angle the light fell over the subjects' shoulders, I prefer the after versions. Finally, if you think the denizens of Shorpy only glance at the photos, you must not read the comments. Some folks pore over the photos and pull out some amazing details.