# How can I understand is the picture $2D$ or $3D$

I can not understand is this picture 2D or 3D. What is the rule or condition to be a 2D or 3D picture. How can I understand that? Please help me!

• Are you referring to the fact that this is an "impossible" 3D object ? youtube.com/watch?v=gj77fu2EcKg
– user65203
Apr 9 '16 at 15:53