An imaging device for sequentially imaging a portion of a continuously moving web to provide a digital data stream which is then analyzed by a single computer without the used of dedicated signal processing hardware. Techniques for operating on the data stream from an imaging device are disclosed, particularly including operations based on blob information stored in terms of starting position and segment run lengths in a crossweb direction. These allow definitions of blobs to be accumulated in a line-by-line fashion, and allow classes of defects commonly found in continuous web manufacturing to be identified with far less computing power than was previously required. In particular, in the challenging application of inspecting flexible circuits, data rates in excess of 10 mega-pixels/second are achieved and successfully processed.