Yes, I think this photograph of the Post Trader's store was taken by Private Howard. It has been published a number of times now, generally without any reference to the photographer. I am traveling and do not have my research files with me, but as I recall, the original image does not have Howard's marking on it, but I think it is listed in Howard's catalog of views. There were a number of photographers at the Red Cloud Agency/Camp Robinson in 1877 so it is possible that it was taken by someone else. Until a second example of this image turns up with markings, we cannot know with certainty.
The Denver Public Library also has an earlier photograph of the Post Trader's store, taken circa. 1875. There was a photographer named Mr. Thomas who came to Camp Robinson at the time of the treaty council. Would love to find more out about him.
The Library also has a number of other Howard images, including one of Crow Butte. The Huntington Library has recently also put up its collection of Howard images as well.