To say we need pics rendered at 300 ppi/dpi is not info enough. That's called... "The horse, bridles from the back."...
They should also say what  the resolution(s) should be .
 
Example:
20in x 20in would be 6000 x 6000 ppi/dpi...right?

                                                                          

Only 3D and Bryce, comes at my pictures!!!