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Due to the growth of computer crime, an important and urgent problem is the development of methods for detecting the integrity violations of a digital image. In particular, the detection of different types of the image post-processing after their possible forgery is a grey area of information security, and the detection of processing by the Sharpen Filter is an issue practically not covered in open scientific literature. The artificial sharpening of a digital image is the reverse procedure to the blurring. Previously, the authors of the paper developed the method for detecting blur of a digital image based on an analysis of the growth rate of singular values. When blurring, the growth rate of singular values is an order of magnitude smaller than before the blurring, which makes it possible to reveal a threshold value for detecting blurred images. The singular values increase accordingly to the artificially sharpening. But it is not possible to reveal the threshold value in this case. The aim of this paper is to identify the parameters of the digital image matrix, which indicate an artificial sharpening, and to develop a method for detecting sharpness as a digital image post-processing. If the contour is considered as a change in the brightness function of a digital image, then the change in the brightness function will be faster when the contours are sharpened. If two adjacent pixels had the close sharpness values before sharpening, then applying this filter will increase the difference between them. In this paper, the investigation of the close color pairs of an image is carried out when the Sharpness Filter was applied to it. It is revealed that the number of close color pairs during processing decreases. The threshold value which allows separating the processed image from the raw one is empirically established. The method of detecting sharpness as a digital image postprocessing is developed based on the results obtained. [ABSTRACT FROM AUTHOR]

The protection of electronic information by cryptographic and steganographic methods, as well as their combination, is in great demand today. However, the new type of steganography - hash-steganography, fundamentally differs from classical steganography in that there is no need to embed messages in a container, no need to worry about the amount of information that can be transmitted in one container without compromising the visual stability of the image. A certain sequence of ordinary digital images is a message. The purpose of this work is to increase the efficiency of transmitting a secret message by modifying the hash-method of steganography. Previously, algorithms for obtaining hash functions of digital images have not been used to transmit messages, but they have found their application in hash-steganography. This paper compares two algorithms for obtaining hash codes and suggests a method of their application for transforming a text message into a sequence of digital images. It is a certain order of files transferred that is decisive in the decryption of a message. The symbols of the message are put in correspondence with the part of the hash code of the digital image. Thus, the necessary combination of files is formed, the number of which is equal to the number of symbols in the message. A comparative analysis of the two algorithms of the method has been performed. The results obtained have confirmed the effectiveness of the hash code algorithm based on the analysis of digital image DCT coefficients. This algorithm makes the method resistant to attack by compression, changing brightness and contrast, magnification and rotation. [ABSTRACT FROM AUTHOR]