Inclusion of picture in service_template API

[goforgold]

By default, I do not get any any field picture/image/picture_id/image_id in the response of Service Template.

My URL
{host}/api/service_catalogs/3000000000001/service_templates/?expand=resources&attributes=dialogs,currency

When I include picture in attributes, I get below error

{
    "error": {
        "kind": "internal_server_error",
        "message": "source sequence is illegal/malformed utf-8",
        "klass": "JSON::GeneratorError"
    }
}

I see we have separate endpoint for /pictures. But how do I know the ID of the picture which is associated with specific service_template?