Here’s 13000+ lines of API specification and examples (from which the reference is created).
A search reveals no such named method on any endpoint, so I don’t know what you could be referring to.
The last little function produces the chat completion image part that can be added to a content list such as this, for multiple items with images:
"messages": [
{"role": "system",
"content": [{"type": "text", "text": "Hello robot"}]
}
]