The sample values of a digitized image (14) are encoded utilizing the amount of redundancy in the digital data to generate check bits which are attached to blocks of the data prior to transmission or recording (Fig. 2A). After transmission or recording, the recovered data is re-encoded using the original encoding rules, and any resultant errors which have changed the redundancy are reflected in the re-encoded check bits (Fig. 2B). The original check bits attached to the data are compared to the re-encoded check bits (26) to determine if the errors are correctable (27), and, if so, what steps must be taken to correct the errors (30) and to restore the original redundancy to the recovered data (31).