Some of our products have incorporated third-party images (for example the Scientific America Ad Brushes). Almost all of these images are in public domain. Some images have been purchased with the right to reuse them and to incorporate them in new work, thus these new works are derivative works. Where the use of such work is restricted, we have studiously followed those restrictions, or we have not used the work. Where credit has been required we have given it. We have not claimed copyright except when it is both possible and appropritate.