A system for facilitating copyright protection of material includes an apparatus for detecting the presence or absence of a block of data, which may have been embedded repeatedly a predetermined number of times in the material. The presence or absence of the data block is detected from data representative of versions of the data block recovered from the material. The apparatus comprises an accumulator operable to combine the value of the bit at each corresponding position within each recovered version of the data block to generate for each bit an accumulated score. A detection processor is operable to compare the value of the accumulated scores for the bits of the block with at least one threshold, and from the comparison determine a total number of detected bits of the data block. The detection processor declares the data block as being present or absent in dependence upon the total number of detected bits. For example, the detection processor may compare the determined total number of detected bits with a threshold determined with respect to the total number of bits in the data block. If the determined number of detected bits is greater than the threshold, the detection processor determines that the data block has been detected, and otherwise determines the data block as being absent. Accordingly, the copyright protection system is provided with an improvement by reducing a probability of falsely detecting a data block as being present when it is not, and reducing a probability of not detecting a data block which has been embedded in the material. Furthermore, the system does not require knowledge of the content of the embedded data, to determine whether or not the data has been embedded in the material.