Why Are These Ring Structures Considered Diastereomers?

[NY152]

Could someone explain to me why the ring structures in this photo are diastereomers? From looking at them, I see a plane of symmetry, and no chiral centers so I'm unsure how they're diastereomers without have R/S characteristics

 

[mjc123]

They are cis-trans or geometrical isomers. I believe these days geometrical isomers are classified as a subset of diastereomers. Chiral atoms are not necessary for diastereoisomerism.