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There are metadata approaches that are specialized for images or a given media content type such as YouTube video.
Some of them are provided in the markup, while others are embedded into binary files such as images.
Image Metadata and XMP
Digital photographs and custom images form integral parts of web sites. Various types of metadata can be provided
with them, including descriptive, technical, and administrative metadata.
An advanced approach is to provide image metadata by markup. The alt attribute is vital for validity. Properly
provided attribute values can improve accessibility too (see Chapter 10). The longdesc attribute, however, which
could be used to provide a link to a long description for images and other nontext contents, has poor software support
and is obsoleted in (X)HTML5.
Beyond the image descriptions provided in markup and the descriptions or image licensing written in RDFa
discussed earlier, advanced and professional image manipulation software such as Adobe Photoshop can be used
to add or modify metadata contained in the image files themselves (Figure 7-4 ). To a limited extent, file explorers of
modern operating systems can also perform this task.