Though this image is subject to copyright, its use is covered by the U.S. fair use laws because:

1. It representatively illustrates an educational article about a once popular, once widely-appreciated comic strip series of the past; its inclusion in the article adds significantly to understanding it because it is a historical sample of the art and story that are the subject of the article, and is specifically referred to in the critical commentary.
2. The image is used as the primary means of visual identification, and/or confirmation of the reader’s memory of the article topic.
3. It is of much lower resolution than the original (copies made from it will be of very inferior quality unsuitable for any commercial purpose).
4. It is not in any way replaceable with an uncopyrighted or freely copyrighted image pertinent to the article subject, because the whole body of work under discussion is copyrighted.