The aim is to use an ESP32 for image capture and data transmission to the smartphone using Bluetooth.

In order to ensure that the data rate was acceptable, a proof of concept was created using an ESP32 camera dev board.  We could not find any examples of Bluetooth camera data transfer using the ESP32 but we were able to produce a simple demo based on the Bluetooth serial port example provided by Espressif. Using the esp32-camera library, we were able to get a quite reasonable frame rate over Bluetooth to an android smartphone at VGA resolution.
I have made the Bluetooth camera code for the ESP32 available here.

Code for receiving the video stream on Android is available here.