Is it possible that this standard american bulldog is pure bred and not mixed with a pit bull? pics?

Definately not pure American Bulldog, and defiantely has pit in it's pedigree. Many bulldogs with cropped ears are mistaken for pits, but you can usually tell by the eyes and length of snout. Solid brindle coloring is also somewhat unusual for an American Bulldog. Very likely a cross somewhere in the line. Good looking boy though.