This is Heinrich Rudolf Hertz's autograph, from <i>Oliver Heaviside: Sage in Solitude</i> (<a href="//commons.wikimedia.org/wiki/Special:BookSources/0-87942-238-6" title="Special:BookSources/0-87942-238-6">ISBN 0-87942-238-6</a>), p. 111. The image is reprinted courtesy of the Burndy Library (as stated in the credits in the back of the book, p. 318), but its age implies that it's public domain. (It must have been made in 1894 or earlier.) It was scanned on an Epson Perfection 1250 at 400dpi, cleaned up (some text was showing through the back) in Photoshop, reduced to indexed grayscale, and saved as PNG using the 'Save for Web' optimizer.
<p>Heinrich Rudolf Hertz
</p>
<ul><li>The original uploader was <a href="https://en.wikipedia.org/wiki/User:Grendelkhan" class="extiw" title="wikipedia:User:Grendelkhan">Grendelkhan</a> at <a href="https://en.wikipedia.org/wiki/" class="extiw" title="wikipedia:">English Wikipedia</a>.</li></ul>
circa 1894 <div style="display: none;">date QS:P,+1894-00-00T00:00:00Z/9,P1480,Q5727902</div>
<ul><li>28 July 2004 (original upload date)</li></ul>
Transferred from <span class="plainlinks"><a class="external text" href="https://en.wikipedia.org">en.wikipedia</a></span> to Commons.