Thanks to the photographers listed below for their photos available through https://www.flickr.com and Creative Commons licensing. Thank you to the following photographers for their images available under Creative Commons license attribution 2.0 Generic (CC BY 2.0).
Any images available from https://www.needpix.com (a royalty free, public domain images website) are listed specifically.
These credits are not in any particular order.
Image Trains by Nick Nunns. Image no longer available.