The pictures I checked for oak and yellow poplar had rougher bark than that plus the white oak seemed slightly darker. You may need to slice some off and do like Dan suggested. Also, taking a piece and cutting iut into a rectangle then measuring dimensions and weighing it would give specific gravity which could help too.
Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.