There are situations where it is useful or required to handle pure binary content using the same framework as other resources. Typically, this is when the binary content is referred to from other FHIR Resources. Using the same framework means that the existing servers, security arrangements, code libraries, etc. can handle additional related content. Typically, Binary resources are used for handling content such as:
- CDA Documents (i.e. with XDS)
- PDF Documents
- Images
A binary resource can contain any content, whether text, image, pdf, zip archive, etc. These resources are served in their native form on the rest interface, but can also be represented in XML, JSON, or other formats, such as when including these resources in a Bundle (used when it is convenient to include these in the response directly rather than leaving them by reference).
http://hl7.org/fhir/R4/binary.html