This is a derivative image. I have taken an (in many ways excellent) image uploaded by wiki-contributor David Hunt and rotated it a little. I find this angle less challenging. I hope David Hunt will forgive me. For the unconvinced, and any others interested, here is the original:
Licensing
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I, the copyright holder of this work, release this work into the public domain. This applies worldwide. In some countries this may not be legally possible; if so: I grant anyone the right to use this work for any purpose, without any conditions, unless such conditions are required by law.