Vertical and horizontal lines are an element of Mondrian's art symbolized harmony between opposites.
The first one can be seen either way. For me, I saw a vase first. In all of the pictures, the black drawing is considered the positive space and the white background behind it is considered to be the negative space. If you look at the vase picture again and imagine the background to be the black portion, you see two faces.
Hope this helps! :)
