This image is a modified version (the original had a calendar saying "Cat's Day Off" and the rats were pink) of one which comes from the Art Today commercial clipart website, and is © 2000-present www.arttoday.com.

Art Today lists the source as CreaticomB: Cartoons Domestic 02 (presumably a directory on a clipart CD), published by Creaticom, Inc.. The artist is not given.