Help needed in the postman's setup

Context

Okay, let me set a context first. I recently worked on a project to create a Postman workspace for Rest API requests to the Geminii models for various works. You can study more about the project on this Gist.

Guidance I Wanted

Curl code In this codebase, we are converting the image to base64. How can I achieve this automatically in Postman, as mentioned in the gist?