creating a custom message type including an image

I'm trying to define and use a custom message type. This message will include a few primitive data types as well as a sensor_msgs/Image.msg type for transferring the image. I have not managed to work out how to define this last element yet. Do I need to update the package dependencies somehow? What type name would I use for this. I'm assuming this is even possible, if not would I need to make a copy of what's in the sensor_msgs/Image.msg instead. Thanks