On first appearance, it looks as if this pen and ink drawing has been photographed in its frame. However, close inspection shows that the diagonal lines at each corner of the image are not the joints of a frame.
The white lines are in fact pins used to secure the print and prevent it from moving during the photographic exposure. The pins have been set at an angle so that they don’t obscure the image.
The finished negative could be trimmed in to the image so that the pins are removed and no longer appear in the finished positive print.