We at IPTC are working with the schema.org team to create a definitive mapping between IPTC embedded photo metadata fields and their equivalent schema.org properties.

Out of that work has come a couple of suggestions for new properties which aren't covered exactly in the current schema, and suggestions for clarifications.

• New property on CreativeWork: https://schemaorg/copyrightNotice
  Description: Contains any necessary copyright notice for asserting the intellectual property for this Creative Work and should identify the current owner of the copyright for the Work.
  rdf:type: https://schema.org/Text

• New property on CreativeWork: named either https://schema.org/creditLine or https://schema.org/creditText
  Description: The credit to person(s) and/or organization(s) which is required be used when the Creative Work is published.
  rdf:type: https://schema.org/Text

We also have some requests for clarifications in the docs:

• Make it clear when to use “author” and when to use “creator”. Currently the definitions seem to overlap. Can we make it clear when each property should be used?

• Make it clear when to use “description” vs "abstract" and “caption”. Currently ImageObject defines caption but also has description which is inherited from Thing, plus abstract inherited from CreativeWork.