When I print a trimmed picture from the Model space with vector output selected, I get a mask overlaid on images that were trimmed with a circle or a curve. There are no issues with pictures that were trimmed using a rectangle.
If I print from Layouts view, the problem occurs not only in vector printing mode but also in raster.
I found the ticket RH-34639 seems to deal with this problem. But it is marked as Obsolete, even though the problem persists.
I also tested different image formats, but the issue seems to affect all of them.