問74
頻出度★★★
電子透かしによってできることとして, 適切なものはどれか。
平成22年度 春期 ITパスポート試験 問74
This question's explanation and your answers so far.
解説
問 74
Incorrectア
Saying that data cannot be used without a decryption key describes encryption. Encrypted data cannot be read without the key, whereas data carrying a digital watermark can still be played or viewed without any key, and it looks and sounds almost unchanged. A digital watermark is not a mechanism that stops the data from being used; it is a mechanism that embeds information, so this choice is wrong.
Incorrectイ
Displaying the information as a see-through image overlaid on the original image describes putting a faint logo or the word SAMPLE on top of a preview image, which is not the essence of a digital watermark. A digital watermark embeds information inside the data so that the change cannot be noticed; a mere overlay spoils the appearance of the original image and can easily be removed by cropping or replacing it, so it does not serve as proof of copyright.
Incorrectウ
Limiting the number of times data can be copied is a function of DRM (digital rights management) or copy protection. A digital watermark only embeds information; it does not forbid the copy operation itself or count how many copies are made. There are applications in which a playback device reads the embedded information and uses it for copy control, but the count-limiting function itself is not provided by the watermark, so this choice is wrong.
- エ
正解 The correct answer is エ. A digital watermark embeds information such as the copyright holder name, the creation date, or the terms of use into the data itself — images, audio, video, documents — in a form where the human eye or ear cannot tell any difference from the original data. The embedded information can be extracted with dedicated software, so even if the content is copied or reposted without permission, it can later be proven whose work the data is. Choice エ states exactly this definition — embedding the creation date, copyright information, and the like so that the change from the original data is not apparent at a glance — so it is appropriate.
ここがポイント
- A digital watermark embeds copyright information, creation dates, and the like into the data itself in a form whose difference from the original data cannot be perceived. The information remains even after copying or reposting, so it is used to prove the origin of a work and to protect copyright.
- The question tests telling apart technologies with similar aims. Remember them by their roles: encryption = the content cannot be read without a key; DRM / copy protection = copying or playback is restricted; digital watermark = information is embedded unobtrusively.
用語