Our method which uses the public-key cryptography over digital signature has a number of advantages: 1 It is difficult to detect the encrypted random estimator signal which is required for extraction of the source information from the image. Hence, we are able to ensure the integrity of the metadata and its authenticity.
This ensures that a hacker would not be able to easily separate the header, delete it, and create a new one. We took a multi-layer watermarking approach to increase the data-hiding capacity, as opposed to single-layer watermarking schemes.
This is possible because the watermarking technique is fully reversible. In our scheme, the first layer stores information related to the source and information used to check the integrity of the image and message.
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The second layer is designated for a tamper localization function. Because of the reversible nature of the scheme, it is possible to watermark over the two layers and subsequently retrieve information from the first layer by removing the second layer completely. This greatly increases the amount of data that can be embedded. The reversible watermarking scheme enables a tamper detection function to be incorporated.
Tamper detection is achieved by comparing the CRC of non-overlapping block embedded and the CRC of the corresponding block after dewatermarking. Using the tamper detection function, it is possible to determine where modifications were made to an image. However, digital signatures can only detect the presence of tampering but cannot localize the tampering in the image.
Using our scheme, it is possible to locate where tampering has been performed in the image.
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This added functionality will be very useful for doctors and legal professionals to detect any attempts that have been taken to tamper with the image or the watermark. We recognized that the processing time needs to be significantly reduced before the scheme could be deployed for practical clinical use. Matlab which is not the optimum programming language to develop real-time software was used to rapidly develop the prototype program to test the concept. Furthermore, our focus in this paper is on single image.
Future work will involve modifying the scheme to handle multiple images or volume dataset so that the images can be watermarked in a reasonable time. To avoid under and overflow, our scheme shifts pixel values of images by four gray levels values because many modalities produce images that do not utilize the full bit range of pixel values. However, it is still possible that there might be images that utilize the entire bit range of pixel values.
For such images, shifting the pixels by four gray levels will not be possible. Hence, to avoid under and overflow for such cases, one possible method is to first check whether the pixel value is 0 or at the maximum allowable pixel value for the image. If the pixel selected has one of these two values, the pixel will not be modified. This method may not be optimum, but it will avoid under and overflow, and it is simple to implement.
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However, a small drawback to this method is that the embedding capacity will most likely be slightly reduced. In this study, we have focused on studying images with unsigned pixel values. DICOM also supports images with signed pixel values. The scheme proposed can be modified to handle signed pixel values by shifting the signed pixel values into the unsigned pixel range before watermarking and restoring the values back to the signed values after watermarking.
We have mainly tested our scheme based on the scenario in which there is a single recipient, and the recipient is known once the image is acquired by the sender. In certain scenario, the recipients of the images are not known beforehand, and the images will need to be archived first. In such scenario, a special archive public key could be used to first secure the images. The process could be handled by the archiving system. The corresponding private key should only be handled by authorized personnel who have the rights to retrieve the images from the archive.
This whole dewatermarking and dewatermarking process could be managed by the archival system. There could also be instances where the images need to be sent to multiple recipients. In such situations, two possible approaches could be used. In the first approach, multiple copies of the same image but watermarked using the public key of each recipient respectively will be sent.
This first method can be considered as a one-to-one approach. A second approach is to use one common public and private key for multiple recipients. Using this approach, the recipients will most likely be grouped into a workgroup which will share the private key. This can be considered as a one-to-many approach. The second method involves managing workgroups and has an added difficulty in ensuring the security of the common private key. The first approach will provide better security because private keys are not shared.
This infrastructure is based on the image security system proposed by Cao et al. This includes secure exchange of DICOM information over open networks and logging of security information e. When a sender needs to send an image to a recipient in another hospital, a request for the public key will be sent to the PACS security server which keeps a log of the activity of every watermarking operation.
The image will then be watermarked using the public key before sending to PACS security server. Once the image reaches the other hospital, the PACS security server at the other hospital will receive the image which will subsequently be sent to the recipient workstation. An illustration of how the proposed scheme could fit into the overall PACS.
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Medical image security has become an important issue as images are communicated over open networks. However, there are no established techniques that can fully address these issues to be deployed in a hospital information system. In this paper, we described a reversible watermarking scheme which could be used to address the authentication and integrity problem of medical images.
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J Digit Imaging. Published online Apr PMID: Corresponding author. This article has been cited by other articles in PMC. Abstract Teleradiology applications and universal availability of patient records using web-based technology are rapidly gaining importance. Key words: Digital watermark, security, image authentication, teleradiology, public-key cryptography.
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Introduction With the advent of teleradiology, there is an increasing need for doctors to transmit images to healthcare professionals all over the globe to seek high-quality diagnosis or second opinions. Image Preprocessing In the image preprocessing module, underflow and overflow conditions are being taken care of to ensure that the selected image is suitable for the watermarking procedure.
Data Embedding and Data Extraction The embedding process seeks to protect the source information e. This random signal is hereby called the random location signal. The use of a random location signal is to ensure that it will be more difficult to decipher which estimator is used. Only one pixel is designated as the estimator in each block.
cumesouva.cf Open in a separate window. If is NOT satisfied, then the distance between estimator and a is increased by 2 by changing a. The process repeats until all the message bits have been embedded or all the blocks had been processed. Tamper Detection and Localization Integrity of our proposed system is controlled by incorporating a feature known as tamper detection and localization function.
Results Overview of Performance Measures Sample medical images i. These include: Embedding capacity: A measure of embedding capacity is necessary to ensure that sufficient authentication information can be embedded into the image. Imperceptibly : This is to test the quality of the medical images in terms of the invisibility of the watermark.
Robustness to tampering: This measure addresses the effectiveness of the tamper detection and localization function to alterations of pixels. Embedding Capacity The number of bits that can be embedded for the four test images ranges from 74, to , bits. Run Time Time taken for watermarking and dewatermarking process is an important factor to consider for practical use in hospital system. Robustness to Tampering In order to demonstrate the tamper localization function in detecting forgery, counterfeited images were created by manually modifying the pixel values in the watermarked images using image processing software—ImageJ.
Discussion This paper presented a fully reversible dual-layer watermarking scheme that has a tamper detection and localization capability.
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