As ever I preface this asnwer with the observation that you don't mention what platform you are running Splunk on, and this is always significant to the answer to this sort of question.
If you are running on a distribution of Linux (or some other *nix with GNU tools available) your best answer would be to use "curl" to download a local copy of the image to a statically named local image, provided you could somehow identify what the image was called. In this case you also do not specify how you would identify the image. To be honest this sounds like a much broader question than "how do I do X in Splunk", and more about generic sysadmin skills.
