What is a good EXIF/IPTC metadata field to store a general URL about the topic or content of a photo. For example a photo showing the Eiffel tower might have the URL http://www.toureiffel.paris/.
So what is a good metadata field to store fthis? The "standard" description fields like
Caption-Abstract/Description I do not want to use, because they might contain other detailing text to the photo (see this question); I rather thought of using a tag like
SpecialInstructions or maybe
Is there a field which is typically used this kind of URLs?