Best practice for passing images with Phenopacket

Hi folks,

thank you for a super useful resource! We a bit new on the track, and currently find ourselves more or less having to pass a couple of images along with certain Phenopackets - primarily radiography evidence for exchange external to the hospital, where it would be super smooth not to have to trade multiple files.

Is there already a best practice for this, e.g. serialising as a Measurement, as a [data-URL](https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/Data_URLs) in an Evidence ExternalReference or File? Anything to avoid that would most certainly break other service? Thank you kindly!

I guess this is pretty similar to #143, but we would ideally like to be able to do this in the short term, with minimum discomfort for later changes. All the best!