(from the DOJ comments section)
"The Department understands that it would not be possible to track or maintain records of dynamically generated URLs.

The rule is updates the requirement from the previous version of 2257 "expressly to include Internet depictions by requiring that this indexing also include any static URLs associated with depictions of tha tperformer and to maintain a copy of the depiction with the static URL associated with the depiction.

so the way i read this.. if you have a dynamic website, you can put the location of the images as the root domain or the root of the sub domain that the images are dynamicallly generated on and you are covered

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