Apparatus for inspecting a container for variations that affect commercial acceptability of the container that includes a light source for directing diffuse polarized light energy through a container while the container is rotated about its axis. A first camera is disposed to receive diff-use polarized light energy transmitted from the light source through a portion of the container, so that the first camera receives an image of the container portion in which opaque variations appear dark against an otherwise bright background. A second camera receives light energy transmitted from the light source through substantially the same portion of the container, and includes a polarizer at cross-orientation to the polarizer at the light source. The second camera receives a bright image of stress variations in the container, which alter polarization of the diffuse polarized light energy passing through the container, against an otherwise dark background. An image processor is coupled to both of the cameras to scan associated images of the container portion viewed by the cameras for detecting and distinguishing between and among variations in the container.