ImageFlow is licensed under the Creative Commons BY-NC 3.0. This means you need the author's permission to use ImageFlow in commercial projects.
If you want to use ImageFlow in a non-commercial project you don't need the author's permission.
If you want to use ImageFlow in a commercial project, you get the author's permission by purchasing a license.
If you plan to use ImageFlow in multiple projects you can purchase a volume package with 5 licenses and save 30%.