Thanks for trying everyone, but no one is correct. Steve, the photo is undated in the book where I found this photo. I believe the author probably got the photo from a descendant, and it's possible the family does not have a date for it.
Hint #4: The book which has the photo when the man was older has been previously mentioned on the forum. This book was written by a member of this forum.
Hint #4.25: In one previous guess, the right conspirator was mentioned in the post, but the person guessing did not ask if this were the right conspirator.
Hint #4.5: The book where I found the photo for this question has been previously mentioned on the forum.
Hint #4.75: The man in the photo has been previously mentioned on the forum.
Hint #5: The book (written by a member of this forum) that has the photo of this man when he was older has been mentioned in one of the previous wrong guesses for this question.