**6. Conclusions**

252 Emerging Informatics – Innovative Concepts and Applications

causes oscillations specially in low percentages of tampering, so the reported percentages

The system described above has a very low complexity, for embedding a watermark of length N, 5N multiplications are needed, the average execution time in a consumer laptop is depicted in Fig. 15. It can be seen that the system clearly meets a wide spectrum of practical needs; one can ensure that the system can process a document with hundreds of pages in

few seconds, which should be good enough for most practical scenarios.

Fig. 15. Execution times for documents as the number of characters varies.

**Document Sample Gain ( g ) Altered Characters ( % )** 1 0.020 0.625 2 0.0140 1.570 3 0.0140 22.76 4 0.0190 2.510 5 0.0120 20.09 6 0.0135 2.003 7 0.0200 12.46 8 0.0160 6.308 9 0.0170 0.675 10 0.0175 0.453 Table 3. Percentage of minimum altered characters the system can determine that the

are those in which the correlation don't crosses the threshold anymore.

document is tampered.

**5.3 Practical considerations** 

Through the development of this work, the following conclusions can be reached: Watermarking DDS format documents is a feasible and low complexity task that accomplishes a reliable electronic document authentication schemes with many desirable characteristics such as imperceptibility and very good tamper detection capabilities. Recall that many works in the field of document authentication are developed considering electronic documents as binary images, thus the development of watermarking systems in script format is a rich research field.

Results show that watermark imperceptibility is highly achieved as described in section 5.1, and considering the results of the MOS test, we can conclude that the proposed watermarking system will meet almost any imperceptibility requirements. Another important achievement is the tamper detection capability, that proved to be reliable even in the worst case of our tests, however, if this is a concern, a future work could perform verifications in smaller blocks, for example, the verification can be done in streams of 100 characters, so the 22.7% of characters that must be tampered, and 23 characters altered out of 100 is more likely to be a harmless modification since would be more difficult to have an attack useful to the proposes of any attacker.

Finally, the scheme discussed in this chapter is not intended to replace any security measures implemented in the different electronic document schemes such as the ones implemented in the ODF or in the PDF, but it would be advised to complement the current ones so a more secure electronic document model could be achieved.
