Most of the photos on this site were extracted from reference images (high-resolution tiffs, 20 to 200 megabytes in size) from the Library of Congress research archive. (To query the database click here.) Many were digitized by LOC contractors using a Sinar studio back. They are adjusted by your webmaster for contrast and color in Photoshop before being downsized and turned into the jpegs you see here.
I believe this was for publicity purposes during the Fifth Liberty Loan drive of 1919 taken in Washington D.C. The Belgians used dogs frequently in WWI to pull their machine gun units. View full size.