Actually Mathew Brady usually sent out his operatives to do all the photographing, and in earlier years Brady had taken credit for all of this work. It is only in the last few decades that researchers have found that many of the photographs were taken by others, such as the USS MONITOR photographs which were taken by James F. Gibson. Andrew Russell had put out an album shortly after the war, of the photos he took, and this album included two of the MENDOTA photos, which even included the date they were taken. Similarly many other recent photographic studies have been able to identify some of the photographers of many of the other photographs taken during the war.
I have no particular connection with the MENDOTA, other than that it was a double ender, and I am interested in this class of gunboats (the SASSACUS class) as the USS AGAWAM, of which I have a major interest in, was one. About a couple of decades ago I purchased four photographs of the AGAWAM, two taken in profile from the bank of the James River, and the other two of officers and enlisted sailors on the vessel. These were from the collection of one of the officers who served on the vessel, and thus were obviously confirmed as being that particular vessel. Yet I had seen one of the photographs misidentified as the MENDOTA elsewhere. The differences could be distinguished on closer examination, and some of these I have pointed out in one or more of my web pages.
Although I have a very basic roll of the personnel of the AGAWAM online, I have been adding much more data to this roster, at my desktop database, from very many sources such as the rolls, census records, military and pension records, etc. Some of the sailors will obviously never have a complete biography, as, no doubt they would have disappeared into obscurity. At least you are able to complete the biographical details for your MENDOTA ancestor, but some of the other sailors will remain a mystery to us, for all time.