I'm willing to bet that if you triggered a spotlight database rebuild that it would be triggered in that process. My guess is that spotlight sees an image to index, ocrs all the text and adds it to the index. It probably also detects qr codes and generates a 'preview' of their content by following the link. Possible it may also do that if you were to take a picture of a url clearly enough that it could be OCRed.
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I'm willing to bet that if you triggered a spotlight database rebuild that it would be triggered in that process. My guess is that spotlight sees an image to index, ocrs all the text and adds it to the index. It probably also detects qr codes and generates a 'preview' of their content by following the link. Possible it may also do that if you were to take a picture of a url clearly enough that it could be OCRed.
You can use the mdimport command-line tool to manually index individual files.