Method of securing graphical data against forgery and tampering comprising the steps of: storing in a memory of a processing unit a graphical data block (210, 310) containing a digital representation of a given finite set of graphical symbols of the graphical data; processing with the processing unit the digital representation of graphical symbols of the stored graphical data block with an error correction code programmed in the processing unit to generate error correction data in a corresponding error correction data block (230, 330); formatting (215, 240; 315, 340) the graphical data block and the error correction data block with the processing unit to respectively provide, in a human readable graphical data block, a human readable representation of the graphical symbols of the graphical data block and, in a machine-readable error correction data block, a machine-readable representation of the error correction data of the error correction data block separate from the human readable representation of the graphical symbols of the graphical data block, to obtain (250, 350) a corresponding verifiable graphical data block comprising said human readable graphical data block and said machine-readable error correction data block; and (i) displaying human readable graphical symbols and corresponding machine-readable representation of error correction data of the obtained verifiable graphical data block on a support being a display connected to the processing unit, or (ii) marking on a support being a substrate, via a marking device connected to the processing unit and equipped with a control unit operable to control the operation of marking based on data received from the processing unit, human readable graphical symbols and corresponding machine-readable representation of error correction data of the obtained verifiable graphical data block received from the processing unit, thereby providing on the support verifiable data comprising the human readable graphical symbols and the corresponding machine-readable error correction data; the method further comprising: calculating with a hash function programmed on the processing unit a hash value of any portion of a data block resulting from a concatenation of the graphical data block and the error correction data block; and storing the calculated hash value as a reference hash value in a ledger. storing in a memory of a processing unit a graphical data block (210, 310) containing a digital representation of a given finite set of graphical symbols of the graphical data; processing with the processing unit the digital representation of graphical symbols of the stored graphical data block with an error correction code programmed in the processing unit to generate error correction data in a corresponding error correction data block (230, 330); formatting (215, 240; 315, 340) the graphical data block and the error correction data block with the processing unit to respectively provide, in a human readable graphical data block, a human readable representation of the graphical symbols of the graphical data block and, in a machine-readable error correction data block, a machine-readable representation of the error correction data of the error correction data block separate from the human readable representation of the graphical symbols of the graphical data block, to obtain (250, 350) a corresponding verifiable graphical data block comprising said human readable graphical data block and said machine-readable error correction data block; and (i) displaying human readable graphical symbols and corresponding machine-readable representation of error correction data of the obtained verifiable graphical data block on a support being a display connected to the processing unit, or (ii) marking on a support being a substrate, via a marking device connected to the processing unit and equipped with a control unit operable to control the operation of marking based on data received from the processing unit, human readable graphical symbols and corresponding machine-readable representation of error correction data of the obtained verifiable graphical data block received from the processing unit, (i) displaying human readable graphical symbols and corresponding machine-readable representation of error correction data of the obtained verifiable graphical data block on a support being a display connected to the processing unit, or (ii) marking on a support being a substrate, via a marking device connected to the processing unit and equipped with a control unit operable to control the operation of marking based on data received from the processing unit, human readable graphical symbols and corresponding machine-readable representation of error correction data of the obtained verifiable graphical data block received from the processing unit, thereby providing on the support verifiable data comprising the human readable graphical symbols and the corresponding machine-readable error correction data; the method further comprising: calculating with a hash function programmed on the processing unit a hash value of any portion of a data block resulting from a concatenation of the graphical data block and the error correction data block; and storing the calculated hash value as a reference hash value in a ledger. calculating with a hash function programmed on the processing unit a hash value of any portion of a data block resulting from a concatenation of the graphical data block and the error correction data block; and storing the calculated hash value as a reference hash value in a ledger.