See: https://cloud.google.com/vision/pricing

Running "Explicit Content Detection" is free if done in the same request as "Label Detection". It appears from https://googlecloudplatform.github.io/google-cloud-python/stable/vision-usage.html that running image.detect_safe_search() immediately runs the request without having the chance to say I also want to run image. detect_labels() in the same HTTP request (to save money and an HTTP round-trip).