there is no builtin way to do this that I know of. I do this in publishing
blogposts from org-mode. i use a filter on links that does this. The
copying code is here:

https://github.com/jkitchin/jmax/blob/master/user/blogofile.el#L115

the results of that code can be seen at http://kitchingroup.cheme.cmu.edu.
I wrote about doing some of this here:
http://kitchingroup.cheme.cmu.edu/blog/2013/09/28/Changing-links-to-files-so-they-work-in-a-blog/

It may not be what you want, but it might help you build your code. I hope
it helps!

John

-----------------------------------
John Kitchin
Associate Professor
Doherty Hall A207F
Department of Chemical Engineering
Carnegie Mellon University
Pittsburgh, PA 15213
412-268-7803
http://kitchingroup.cheme.cmu.edu



On Mon, Jun 2, 2014 at 7:23 PM, zhenjiang zech xu <zhenjiang.xu@gmail.com>
wrote:

> Hi orgmoders,
>
> Is there any existing function to copy files in the external links to a
> specified location when exporting .org file to html? I know org-publish has
> functionality to copy files with certain suffices on defined project, but
> my need is to export single file or single subtree in the buffer.
>
> For example, when I export the following subtree, it would be lovely to
> copy the spam.png to the path I set up.
> * foo
>   [[file:spam.png]]
>
> If there is no function ready to do that, what is the easiest easy to
> implement it? any point to the right direction is appreciated.
>
> Thanks,
> Zhenjiang
>