An example of <a href="https://en.wikipedia.org/wiki/Optical_feedback" class="extiw" title="w:Optical feedback">Optical feedback</a>. Uploaded with permission from <a href="https://en.wikipedia.org/wiki/no:Robert_Haraldsen" class="extiw" title="w:no:Robert Haraldsen">Robert E. Haraldsen</a> ©Profero Grafisk, Norway (<a href="//commons.wikimedia.org/wiki/User:Profero" title="User:Profero">User:Profero</a>)
No machine-readable author provided. <a href="//commons.wikimedia.org/wiki/User:Profero" title="User:Profero">Profero</a> assumed (based on copyright claims).
CC BY 2.5
No machine-readable source provided. Own work assumed (based on copyright claims).