English: This is Dr. John Henry Holliday's Philadelphia School of Dental Surgery 1872 graduation photo, so it is certainly the man. He is here aged 20 years, 5 months. Note that at graduation he wasn't old enough to obtain a license to practice in Georgia (age 21 was required) so he had to serve some additional apprenticeship. The source is "www.freeinfosociety.com" which doesn't provide THEIR source. However, the image is an 1872 graduation image which was published in that year, and court cases have generally decided that historical photos published before 1923 are in the U.S. public domain.