Analisis Penyematan Watermark di Tiga Subband Frekuensi Metode Discrete Cosine Transform pada Gambar Hasil Scan

Abstract

The advance of information technology such as marketplaces, e-money, and insurance are required to upload an identity card file for account verification or for electronic payments. The dissemination of this personal information could be misused by a third party who may able to break into the account users and steal the data. Therefore, protection of this personal data is necessary for authentication. In this study, the proposed technique for protection is watermarking. This watermarking is in the form of a binary image which will be embedded in the identity card file using Discrete Cosine Transform method. Discrete Cosine Transform is a method to change the image from the spatial domain to the frequency domain. Image transformation to frequency domain produces a DCT coefficient value that consists of subband frequency. To meet the criteria for good watermarking, embedding analysis is carried out in the frequency subband (low, middle, high, low-middle, and middle-high for each color component. Pixel coordinates the embedding watermark that is different for each 8×8 DCT block for there is an order of values selected for the DCT coefficient. Imperceptibility and robustness analysis were conducted on 10 scanned images with a resolution of 100 dpi and 200 dpi in BMP format. The results showed that the PSNR value is ≥ 52 dB with a (watermark strength) 0,1 and the average SSIM score ≥ 0,9. In order to maintain a balance between imperceptibility and robustness, a good watermarking should be conducted at a high frequency on green component while for a red component is at low-middle frequency those are susceptible of attacks in the form of brightness +20 and contrast +50 with an average of NCC value ≤ 0,85.