I was pretty proud of an instance where I was not identifying who, but identifying when.
My wife's grandmother (Freeda McCarthy) was a child when she got her photo taken with her family: https://www.wikitree.com/photo/jpg/McCarthy-3823
This is a photo, of a photocopy, of the actual photo, sent to my wife by another family member. (Yes, we'd like to get a digital scan of it at some point.)
We knew which one was her grandmother. She was leaning on her mother's leg. We had a pretty good idea of the children, based on name, gender, and dates. We also knew that one child was missing from the photo.
I went through several stages of research to narrow down and establish when the photo was taken:
The youngest child, Howard, is shown in the photo, below the father. Howard was born in 10 Apr 1916.
We saw that the missing child was missing from the photo because she had died young. This was Harriet, who died 29 Oct 1917.
The father, Samuel McCarthy died 1 May 1918.
So we knew that the photo was between 29 Oct 1917 and 1 May 1918.
But the clincher was with the oldest son, Raymond Roy McCarthy. I discovered a newspaper article in The Miller Press, 8 November, 1917:
Ray McCarthy arrived home Friday on a ten days’ furlough and is visiting at the home of his parents Mr. and Mrs. Samuel McCarthy of Alpha township. Ray was one of the first to enlist from Hand County, being stationed at Jefferson Barracks near St. Louis for some time. He is now located on the Mexican border at Columbus, New Mexico, and states that the two other boys who enlisted at the same time are there also. They are Wm. Neuendorff and Robt. Sherrill.
The 8 November 1917 is a Thursday Which means that Ray arrived home on 2 November 1917 and was on a 10 days furlough. You can see Ray in the photo, behind and between his parents wearing his military uniform.
This means that this photo was taken probably sometime in the week of 2 November 1917 to 9 September 1917, while Ray was on leave. We have now narrowed the time of the photo to a period of a few days.
Because of identifying the date of this photo, the story is deeper and it also means that the circumstances of the photo is a tragedy. Harriet died at the age of 7 years old on 29 October 1917. Ray arrived home on furlough just 4 days later because of the family death. The newspaper article did not explain why Ray was home. But the data tells the story. Everyone in this photo is in mourning and probably still in shock. You can see how their mother, Addie McCarthy, is wearing black, and a choker. They likely wanted to get a photo of the whole family while their eldest son is back home from the military, in case something else happened to one of the members of the family. Remember that the United States entered World War I in April 1917. Perhaps the parents were concerned that Ray might be deployed at some point.
And then it's also sad to think that the father, Samuel, died just 6 months later on 1 May 1918. This means that this family photo is likely the last photo taken of Samuel, and likely the last family photo.
Hence the reason why I would like to get a better copy of the photo and get a real digital scan of the photo. It's very precious, even with such sad circumstances.