We know very little information about this photograph. One of the few things we do know is that it is almost certainly not a prisoner from Andersonville, however. Although the reverse of the image in the Library of Congress' records do state "Returned Federal prisoners from Andersonville prison", they also note this to be erroneous. It isn't a glass negative, as is the case with many Civil War photos, but rather the specific print that they have is dated to "1880 and 1889", which likely a large part of the explanation for how the mistake was made, as Andersonville fills an outsized place in Civil War memory of the war when it comes to prison camps.

The claim is decently well substantiated though, as they tie the photograph to two very similar drawings that were published in Harper's Weekly on June 18, 1864 and themselves based on a larger set of photographs taken of prisoners who were released from a Belle Island, at Richmond, in April - part of an ongoing agreement that gave parole to sick and wounded. The images were originally for the purpose of Congressional investigation of abuses, but more notably published as part of a shocking expose on 'Rebel cruelty' by both Harper's Weekly and Frank Leslie’s Illustrated Newspaper, who published a similar set of images.

Of the two photos reproduced in Harpers Weekly, the doctor included a long letter (Well, supposedly. Some text corresponds to government records, so Harper's Weekly might have been trying to make it seem this was a more personal correspondence than it really was!), noting:

These two pictures are what may be called good specimens of the bad cases which are brought to the hospital from the prisons and Belle Isle. They are from the worst of the cases, and these worst cases form a numerous body. Both are dead.

In the first, this would suggest - although not guarantee - that the subject of the infamous photograph in question did not live long beyond the taking of his picture. Dr. Wallace notes that the two featured images in Harper's Weekly both died. It is unclear whether the photograph we have was the specific basis for either of them, which would guarantee that he died soon after, but even if only one in similar condition, the note goes on to mention that they received roughly 100 cases in such a condition, of which 30 had already died. A report predicted 50 more were likely on deaths door and soon to pass we well, but I can find no corroboration of just how accurate that was.

As far as knowing who he was, the accompanying article gives us the best shot at identifying the subject, but unfortunately falls short. Although it doesn't caption the photos with names, it does include several brief testimonials, included by the doctor who sent it all to Harper's Weekly which I'll quote below.

The first named subject was Cpl. W.M. Smith, a 22 year old Kentukian:

I was captured in September, 1863 ; was on Belle Isle six days and nights without shelter. They took away my blanket and gum-cloth. It rained two or three days. I lay at night in the cold dew and frost. While in prison, after leaving Belle Isle, in December, I got small-pox. I wore the same summer clothes in which I was captured; I lay on the floor; I never had any thing to sleep on or any cover. After I got well of the small-pox I had to wash my clothes, for I had worn them all the time. I came in to this hospital in the same clothes. Diarrhea came on in February.

The second is from a 20 year old Jackson Broshers, who hailed from Indiana:

I was captured December 16, 1863; was two months on Belle Isle; had a piece of a tent over me, but it was full of holes, and the water came through. A good many had no shelter at all; I don't know how many. They took from me my hat and cap, and gave me an old jeans rag hat. They took my overcoat, two blankets, and gum blanket. I had meat but three times on Belle Isle. I think it was mule meat, for I never saw such looking meat, and never tasted any of the same queer taste. I never had enough to eat while I was on Belle Isle; my ration. was not near enough to satisfy my hunger. I got thinner and weaker every day, until in two months my stomach gave out ; and then the weakness came on, oh, so bad ! Well, I had to eat my ration or starve; so I chewed and nibbled it off and on as I could. Then in the last month of my imprisonment diarrhea came on. I came into this hospital on March 24, 1864. I am getting stronger and heavier every day. My weight was about 185 pounds. My height is 6 feet 1 inch.

Dr. Wallace goes on to note the man now weighed 108 pounds, and that after being in their care for 8 weeks. But while this does give us some names to look into, unfortunately it is also a dead end. While this photo is the most famous (My idle wondering is whether because we don't know who it is helped make it the best known?*), it is only one of several, and we have a photograph which is identified as William Smith from the collection, and whose features are definitely different enough to rule out, and likewise one of Pvt. Broshers. Several other photographs exist in the collection giving us the name of Pvt. Isaiah Bowker, as well as one more listed as unidentified, which is the clean source of the sketch on the right in Harper's Weekly (Bowker would be reported as died a month later). Even the photographer who handled these is not definitively known, although likely someone in the government employ (tentative identification of A.H. Messinger seems to be the most likely, but only circumstantial).

We do have one final avenue of inquiry, though, as a collection of similar images formed part of a Congressional report on returned prisoners, which included 8 woodcut illustrations (well, technically two, as the illustrations Frank Leslie's used are the same ones, but that ruins the flow of the piece!. It not only provides us with the identity of the left image in Harper's Weekly, Kentuckian John Q. Rose, who died two days after release, but several more not included. This one in particular, of Pvt. Francis W. Beedle from Michigan, who died a day later, stands out as being in at least a somewhat similar position as the unidentified photograph that we have. No where near enough to use as a basis of certain identification though.

So that, essentially, the closest we can get to identifying that one, particular prisoner, short of someone managing to turn up a missing, labeled negative. The facts that we do know are slim. The Congressional Report tells us some 395 men were paroled at that time, and Dr. Wallace implies to us that about 100 or so were in the condition that the images above attest to, and further that 30 or so had died by that point, and plenty more would do so. We can attach names to about ten of them between the various sources which highlighted the images, but none quite seem to be images based on that particular photograph. So once all likely avenues have been pursued, we end up at something of a dead end - and not even an iron clad guarantee it is from the same group of images. At the least though the context of the photo can take somewhat better shape, but the subject remains something of a mystery, both in identity, and in fate.

ETA: Tracking down a few more sources to cross all the ts and dot all the is

Sources

Cloyd, Benjamin G.. Haunted by Atrocity: Civil War Prisons in American Memory. Louisiana State University Press, 2016.

Collins, K. (1988). "Living skeletons; Carte-de-visite propaganda in the American civil war". History of Photography, 12(2), 103–120.

Giesberg, Judith A. "'Eye of History': Looking at Civil War Prisoners of War" in Lens of War: Exploring Iconic Photographs of the Civil War. ed. J. Matthew Gallman & Gary W. Gallagher. University of Georgia Press, 2015. p. 185

Sanders, Charles W. While in the Hands of the Enemy: Military Prisons of the Civil War. LSU Press, 2005.

Library of Congress, Photo, Drawing, and Print Collection

Narrative of privations and sufferings of United States officers and soldiers while prisoners of war in the hands of the Rebel authorities : being the report of a commission of inquiry, appointed by the United States Sanitary Commission King & Baird, 1864.

REBEL CRUELTY—OUR STARVED SOLDIERS.—FROM PHOTOGRAPHS TAKEN AT UNITED STATES GENERAL HOSPITAL, ANNAPOLIS, MARYLAND. Harper's Weekly, VOL. VIII.—No, 390. June 18, 1864 p 385-386

Reports of the Committee on the Conduct of the War - Fort Pillow Massacre, Returned Prisoners. Congressional Printing Office, May 5, 1864.