How to send local image to chat using incoming webhook

[manirhel-zz]

Facing issue while send the local image to google chat room using web hook. please find the code below. kindly help.

attachment = open("images.jpg", "rb")
bot_message = {"cards": [{ "sections": [{"widgets": [{"image": attachment}]}]}]}
print (bot_message)
message_headers = {'Content-Type': 'application/json; charset=UTF-8'}

Error:

TypeError: Object of type BufferedReader is not JSON serializable

Thanks!