This portrait can be found in Grandma's house in You Can't Guess by Carl Barks.
It could very well be an older version of the duck in the portrait which I posted about before. In addition, this duck-man looks similar enough to Dabney from Rosa's Lo$ 10 that I imagine the two to be the same character.
Do you know, Johannes A. Grote's treealmost agrees with you? In that tree this portrait is used to depict Donald's grandfather, but, of course, Elvira is Donald's aunt in that tree, so he's not her husband, but rather Mr Wasserhun, her father-in-law (being the father of the husband of Elvira's anonymous sister, mother to Donald).
He is also, because this tree is goddamned weird, the father of Cuthbert Coot and of Gladstone's anonymous mother. And he is the husband of Daisy's aunt, Griseldis. And his sister marries Ratchet Gearloose and is Gyro's grandmother. (Because Gyro's paternal grandmother has since been identified as "Martha Bird" by the Italians, we can translate Mr Wasserhun as Mr Bird.)
Do you know, Johannes A. Grote's treealmost agrees with you? In that tree this portrait is used to depict Donald's grandfather, but, of course, Elvira is Donald's aunt in that tree, so he's not her husband, but rather Mr Wasserhun, her father-in-law (being the father of the husband of Elvira's anonymous sister, mother to Donald).
He is also, because this tree is goddamned weird, the father of Cuthbert Coot and of Gladstone's anonymous mother. And he is the husband of Daisy's aunt, Griseldis. And his sister marries Ratchet Gearloose and is Gyro's grandmother. (Because Gyro's paternal grandmother has since been identified as "Martha Bird" by the Italians, we can translate Mr Wasserhun as Mr Bird.)
God, I love this tree.
Oh, I am well aware! I, however, do not agree with him! ^^ I share your love for that tree, even though I have many problems with it. I find the idea of placing the background-portraits in a family tree a fascinating one. However, it seems Grote was more concerned with putting a face to as many relatives as possible, rather than identifying the portrait-people in a logical way. For example, the goose-man who is placed as Gladstone's father's mother's father on the tree was originally a portrait hanging on Donald's wall... Why would Donald have a picture of that guy? It's his aunt's husband's grandfather!