You've got two options.

1. Easy: Write python module under REST interface and accept image as form data input and returning class as the API response. This Python REST API is called inside Go API and return the python API response as the Go API's Response.
2. Advanced: Use RPC for cross language communication. Checkout Apache Thrift, gRPC by Google. You might've to use shared Producer-Consumer File DB service.

Based on your complexity use the suitable approach. Usually first approach solves the problem in most of the cases unless you've high scale/concurrency requirments where REST will be an overhead. Additionally, you better introduce a queuing system in either of the above approaches to avoid blocking on webserver.

Cheers!

You could just make a standalone Python module that classifies images and outputs their class. Then call this from Go as an external command. It doesn't seem like a lot of integration is needed, so I'd go with this simple approach.

(You might also consider just using Python for the api server. Nothing against Go but it sounds like a simple layer so maybe that the language doesn't really matter.)