Mark,
Are you refering to this image:
http://www.racinehistory.com/manupics/civilabe.jpg
If so, I believe it may be in the possession of the Wisconsin Veteran's Museum.
In the book
old Abe The War Eagle (Richard H. Zeitlin, Madison, WI: The State Historical Society of Wisconsin, 1986) that image is shown on page 34, and credited to GAR Memorial Hall. Awhile back, GAR Memorial Hall became the Wisconsin Veterans Museum, and Zeitlin is the director of the Museum. They have a larger copy of that image hanging in the front lobby of the museum. I believe Wisconsin museums have a program to purchase the rights of a image for person use or publication, but you'd have to contact them for the details on that.
I highly recommend the book. It describes Old Abe from his hatching to his war service, to his wartime propaganda service to his post-war Republican and GAR propaganda service until his death. It also is a good review of the service of the 8th Wisconsin. Fun Eagle Fact #1: The 49th Wisconsin also had an eagle mascot, a Golden Eagle named Timothy. Timothy's name was changed twice, first to Phil Sheridan, then to Andy Johnson. Both eagles were given to the state after their service in the field. Andy was never tamed to the degree Abe was, and the two would fight quite often. Andy wounded Abe once, and in 1873 Abe got his revenge, wounding Andy. The injuries probably resulted in Andy's death the next year. (Zeitlin, pg 84-84).
BTW, that is my FAVORITE image of the war. Beyond the uniqueness of having Old Abe on the perch, it's a great example of lack of uniformity in a western regiment at the time of the Vicksburg campaign. It shows dress coats, a fatigue blouse, dress hats, a couple of civilian hats, and (gasp) use of both Springfields and Enfields in the regiment. Fun Eagle Fact #2: Bald Eagles aren't born with white heads. Abe's head didn't turn fully white until during his veteran furlough in 1864. (Zeitlin, pg 64).
The Museum's website:
museum.dva.state.wi.us/
The Museum's online gift shop,
Old Abe the War Eagle is available there:
museum.dva.state.wi.us/Ser_giftshop_items.asp