Carl Barks liked making front covers. He made a colossal number of front cover sketches for the Disney comic book series, many more than were actually published. Some he discarded himself and some were sent to the publisher who rejected them. In those days it was quite normal for Barks to mail 10 gag sketches to the publisher at a time, and then he would perhaps choose one or two for publication. The rest were scrapped!!! No telling how many perfectly good ideas and sketches went into the publisher's wastepaper basket...
Not many of the rejected front cover sketches have survived, but the sub-pages will present you to a few that were shelved by Barks in his reference archive. If you are interested in a complete showing of Barks' published covers you should look HERE.