English: United States Forest Service photograph 178352, taken August 20, 1923 by L.A. Barrett for the USFS. Forest officers heliographing from Black Butte fire lookout, in California National Forest (now Mendocino National Forest), California. The standing forest ranger is using binoculars, the kneeling one using a heliograph. The dual-tripod heliograph is that developed by the US Signal Service, and uses a six-blade shutter on one tripod to modulate sunlight reflected by a mirror on the other tripod into dots and dashes for communications.

References:

Photo posted on Flickr on the official feed of the US Forest Service, USDA, at https://www.flickr.com/photos/usforestservice/41719655660/, with this information: "Forest Service, USDA 1923XXXX-FS-Mendocino-LAB-178352 Forest officer heliographing from Black Butte lookout. Mendocino National Forest, California. (Forest Service photo by L. A. Barrett). Additional information on this photo from Foresthistory.org is here: https://web.archive.org/web/20160708140952/http://foresthistory.org/research/Galleries/FireCommunications_Gallery/pages/FHS2738th.htm

The file uploaded here was at https://www.flickr.com/photos/usforestservice/41719655660/sizes/o/ and marked Public Domain https://creativecommons.org/publicdomain/mark/1.0/ by the USFS. The USFS determination that this is in the public domain should be correct, because this is an official USFS photo by a USFS employee, and as such is in the public domain of both the US and the country of origin (the US) as: "a work prepared by an officer or employee" of the federal government "as part of that person's official duties." https://en.wikipedia.org/wiki/Copyright_status_of_work_by_the_U.S._government

Regarding the USFS photo reference number - the right half of this photograph is very slightly truncated, so the final digits of the USFS number 178352, are not on the photo itself, but were written below it. However, the reference number is also printed in full in the rendering the USFS published in Dec. 1926, as Figure 24, page 26, of UNITED STATES DEPARTMENT OF AGRICULTURE MISCELLANEOUS CIRCULAR No. 79, WASHINGTON, D. C. DECEMBER, 1926 A Forest Fire Prevention Handbook for School Children The "Red Enemy of the Forest, prepared by the California District of the Forest Service, United States Department of Agriculture, which may be viewed at HathiTrust here: https://hdl.handle.net/2027/mdp.39015086692806?urlappend=%3Bseq=28

Regarding L.A. Barrett: Louis A. Barrett died in 1945 (over 70 years ago), and was assistant regional forester at the time this photograph was taken, per: William S. Brown, "History of Los Padres National Forest S.B. Show, Regional Forester", San Francisco, CA, June 1, 1945, p. 85, which discusses his career in some detail. ( https://lpfw.org/wp-content/uploads/2013/06/19450000_Brown_HistoryOfLosPadresNationalForest.pdf ) . On Nov 17, 1920, Louis A. Barrett, was assistant California District Forester for Lands ("A History of Outdoor Recreation Development in National Forests, 1891-1942", William C. Tweed, Formerly Historian, History Section, United States Deparement of Agriculture, Forest Service, Washington D.C.)pp. 17. 34., United States Department of Agriculture, Forest Service, ( https://foresthistory.org/wp-content/uploads/2017/01/USFS_Recreation_1891_1942.pdf ) In 1935, L.A. Barrett (Region 5) wrote the U.S. Department of Agriculture, Forest Service, work: "A Record of Forest and Field Fires in California from the Days of the Early Explorers ot the Creation of the Forest Service". He became the first supervisor of the Plumas, Diamond Mountain and Lassen forest reserves in 1905. (per: "Fire in the Forest: A History of Forest Fire Control on the National Forests in California, 1898-1956" by Robert W. Cermak, USDA Forest Service, 2005, ISBN 1593514298, 9781593514297, https://books.google.com/books?id=clceAQAAIAAJ&lpg=PA350&ots=GMFTWDXdrH&dq=%22L.A.%20Barrett%22%20%22Forest%20Service%22&pg=PA350#v=onepage&q=%22L.A.%20Barrett%22%20%22Forest%20Service%22&f=false