Client image to perform Google Cloud Vision API tasks over.
Image content, represented as a stream of bytes. Note: As
with all ``bytes`` fields, protobuffers use a pure binary
representation, whereas JSON representations use base64.
Currently, this field only works for BatchAnnotateImages
requests. It does not work for AsyncBatchAnnotateImages
Google Cloud Storage image location, or publicly-accessible
image URL. If both ``content`` and ``source`` are provided
for an image, ``content`` takes precedence and is used to
perform the image annotation request.