<a href="//commons.wikimedia.org/wiki/User:Clindberg" class="mw-redirect" title="User:Clindberg">User:Clindberg</a> turned up <a rel="nofollow" class="external text" href="http://www.antiquephotographics.com/Format%20Types/Stereos/politicalst.htm">this page</a> that identifies the man in the middle as Lincoln's secretary <a href="https://en.wikipedia.org/wiki/John_G._Nicolay" class="extiw" title="w:John G. Nicolay">John G. Nicolay</a> (looks correct based on <a href="//commons.wikimedia.org/wiki/File:John_George_Nicolay_-_Brady-Handy.jpg" title="File:John George Nicolay - Brady-Handy.jpg">File:John George Nicolay - Brady-Handy.jpg</a>), and speculates that the other person is a visiting Englishman.
<div class="fn value">
E. &amp; H.T. Anthony (Firm) -- Publisher</div>
<p>Created: 1860-1880.
</p><p><br>
Coverage: 1860-1880.
Source Imprint: 1861?-1865?.
</p>
Digital item published 1-25-2006; updated 2-13-2009.
This image is available from the <a href="//commons.wikimedia.org/wiki/New_York_Public_Library" title="New York Public Library">New York Public Library</a>'s Digital Library under the digital ID G90F083_042F: <a rel="nofollow" class="external text" href="http://digitalgallery.nypl.org/nypldigital/id?G90F083_042F">digitalgallery.nypl.org</a> → <a rel="nofollow" class="external text" href="https://digitalcollections.nypl.org/search/index?keywords=G90F083_042F">digitalcollections.nypl.org</a>