 SickItImage is an image processing library that implements algorithms and utilities for use in research, education, and industry applications. It is released under the Liberal Modified BSD Open Source License, provides a well-documented API in the Python programming language, and is developed by an active, international team of collaborators. In this paper, we highlight the advantages of open source to achieve the goals of the SickItImage library, and we showcase several real-world image processing applications that use SickItImage. More information can be found on the project home page. This article was authored by Stefan van der Waalt, Johannes L. Schoenberger, Juan Núñez Iglesias, and others.