Our thanks to andrew-neel, brooke-cagle, caleb-woods, ethan-sykes, foto-sushi, helena-lopes, javier-allegue-barros, joanna-nix, luke-stackpoole, mark-skeet, rawpixel, remi-walle, trust-tru-katsande, to other photographers whom we've credited beneath their photos, and to unsplash.com itself, the home of some outstanding artists.

Other photo credits:

The butterfly on the IOLAS logo is based on a photograph by Zeynel Cebeci and is used here under the terms of its Creative Commons BY-SA 3.0 license.