The only photo postcard (postkarte-Carte postale) that I have measures 3-3/8" x 5-3/8". I'ts hand-colored and would be from the period mentioned. To narrow the camera down might be a challenge. The No. 3A Folding Pocket Kodak was popular from 1903 onward. In fact, I use the lens elements from two Kodak 3A's, one set on my 5x7 and I've used a front element on my 8x10.

Early Danish Photographer

Early Studio

Another Studio

Family Portrait

My kind of Studio

1843? a bit early.