send cropped image with kafka plugin

I am using deep-stream to run detector on the image, and than I want to send the cropped images with your kafka plugin.
I see that in the plugin I can send only metadata, and that the image is not passed on.
how can I do that?

You can modify sources/gst-plugins/gst-nvmsgconv/gstnvmsgconv.c


Get yuv buffer and metadata, then create NvDsEventMsgMeta
I think cropped image can be saved in NvDsEventMsgMeta->extMsg

In order to send cropped image with NvDsEventMsgMeta, what is the best way to send with json? Any suggestion to do so?