I would like to know if it is possible to process images that come from an HDMI source (not a camera) with a Raspberry Pi and openCV. Even by using the hdmi to csi-2 bridge (b102), or by using hdmi to usb? Knowing that the HDMI source is NOT encrypted.
No, it is not possible to use the HDMI port on the RPi as a video capture device. The HDMI port on the RPi is an output only port. It can receive some basic status messages (HDMI-CEC), but it isn't able to receive video in.
You can buy hardware that is designed to operate as a video capture device, but in general, it's pretty pricy.