Computers aren’t yet very good at understanding and interpreting images. Presented with two images, one of a horse and another of a tree, in the absence of any other information, a computer would not be able to tell you the difference, or very much else useful about them.

And so we have metadata – literally data about data; textual information that tells us everything we need to know about our images and helps us find them. Metadata allow us to say ‘show me all the pictures of horses, but not the ones with trees in’ and to ...

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