Change the domain of associatedMedia to Thing
http://schema.org/Thing has the http://schema.org/image property to express a simple image URL that represents or is associated with the primary entity, but has no way of expressing other related media such as video or audio objects.
Currently, http://schema.org/associatedMedia, which has a range of http://schema.org/MediaObject and which would otherwise seem suitable for this purpose, has a domain of CreativeWork. This means that http://schema.org/MedicalProcedure and other children of Thing that do not descend from CreativeWork have no straightforward means of including media objects that complement their content.
Change the domain of associatedMedia to Thing. The benefit of this proposal is that we would cover AudioObject, DataDownload, ImageObject, MusicVideoObject, VideoObject, and any other MediaObject subclass that comes into being.
The adjusted RDFS would look like:
<div typeof="rdf:Property" resource="http://schema.org/associatedMedia"> <span class="h" property="rdfs:label">associatedMedia</span> <span property="rdfs:comment">A media object that encodes or complements the item.</span> <span>Domain: <a property="http://schema.org/domainIncludes" href="http://schema.org/Thing">Thing</a></span> <span>Range: <a property="http://schema.org/rangeIncludes" href="http://schema.org/MediaObject">MediaObject</a></span> </div>
Note that the rdfs:comment would no longer include the statement "This property is a synonym for encodings." This is justifiable because a) "encodings" is a deprecated term for "encoding" anyway and b) because "associated media" suggests a looser affiliation with the containing type (thus the addition of "or complement" to the comment) than "encoding" which suggests a stricter relationship and c) maintaining purely synonymous properties where one of the properties has not been superceded is not a best practice, so let's differentiate the properties according to their names.
If we wanted to go further, we could deprecate the roughly duplicated (but more specific) properties by adding "supercededBy" clauses to the likes of image, audio, and video. But let's not go there; keeping the simplest things easy to do has a lot of value, and associatedMedia is most likely to be embraced by those who are seeking to express more than the simplest of structured data.