A little more info from some quick research I did. It looks like these were indeed sold as a set inside individual sleeves in a portfolio. That would explain why many of these engravings survive in nice shape. A link is attached that has some decent information about these images. The photo was taken by the famous Civil War photographer, Matthew Brady, then engraved by J.C. Buttre and presumably sold by him. Your image depicts Doubleday as a Brigadier General(1 star), there are also engravings depicting him as a Major General(2 star). He was a 1 star in 1862 and became a 2 star during 1863. Your item is most likely from that 1862-1863 period. These are obviously beautiful engravings that would have brought these individuals to life during the time. One just like yours sold in 2019 by Mile High Card Company for $30. I'd say if you're in the $20-$50 range you're doing okay for a nice looking period wall hanger.
https://www.williamreesecompany.com/...ores-and-other
(Images not mine)