I'm a conservation student at the Arts Academy in Split, Croatia. Currently I'm working on an Austrian officer portrait signed by Karl Nagl, from 1862. You can see a photo of that portrait on the blogspot of our collegium:
I am still working on the research of the portrait history. However, as far as I know, Karl Nagl was Austrian portrait painter from Wien. If you want, you can send me photos of those paintings via e-mail, I would be very glad to see them.