Inserted reference pictures and snapping

Hi All! There is a problem with the inserted reference images. I inserted a picture of an old book, to copy the ornaments from it. But the snapping always magnetize my lines to to the corners of the picture. You should make the inserted picture's corners unavailable to the snapping option. I need the snapping while I copying the ornaments, so I can1t switch it off. Or is there some alternative way, that could help this problem? Thank you! (In Rhino 3D the inserted picture gets into the background, so it can't be snapped.) Thanks again! Gábor