I have a SharePoint online environment and a requirement to copy thumbnails of the photos uploaded to an asset library to another library. SharePoint stores photo thumbnails in a folder called "_t" in the photos library.

I have tried to use a SharePoint Designer workflow (with the trigger on item creation) to utilize "Call HTTP Service" action to call SharePoint RESTful service http://server/web/getfilebyserverrelativeurl('URL to the thumbnail in _t')/copyto('destination library file URL'). When I try that it errors: "You cannot copy or move files either into or out of a picture library image preview folder." I don't think it makes sense to restrict copying FROM a preview library, but anyway I was wondering if there is another way of copying files. Any other solution to my business requirement is also appreciated.

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We have achieved this requirement with some change. The end result was that the thumbnails got copied to the other library, but not automatically. Instead it needed user action.

We added a script to the page (using content editor WP), which loaded a ECB Menu Item to all the items, which would call a JavaScript function that uses CSOM to copy the related thumbnail from _t folder to the destination library. Quite complex implementation for such an easy requirement!

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