test.py

//////////lambda side /////////////////////////////////////////
//node.js
// function to encode file data to base64 encoded string
function base64_encode(file) {
    // read binary data
    var bitmap = fs.readFileSync(file);
    // convert binary data to base64 encoded string
    return new Buffer(bitmap).toString('base64');
}

var base64str = base64_encode("file_path_name_in_lambda");

const response = {
        statusCode: 200,
        img_base64:img_array,
};
///////////////////////////////////////////////////////////////


/////////client side /////////////////////////////////////////
//python
r = requests.post(....)
img_base64 = r.json()['img_base64'] 
imgdata = base64.b64decode(img_base64)
# save image
with open(FilePath+v1, "wb") as fh:
    fh.write(imgdata)
//////////////////////////////////////////////////