Image_processing can't obtain image from esp32 cam

I have an esp32 cam displaying a stereo amp volume level.
This image_processing device is supposed to read the setting.
But it only fills my log file with
“2019-08-06 08:58:55 ERROR (MainThread) [homeassistant.components.image_processing] Error on receive image from entity: Unable to get image”
running ssocr with the exact parameters you see below displays the correct value.
(This is when the camera is working, of course)

image_processing:
  - platform: seven_segments
    x_position: 0
    y_position: 0
    height: 120
    width: 160
    #threshold: 20
    extra_arguments: grayscale shear 20 rotate 355 crop 40 50 70 40 -fwhite -bblack
    source:
      - entity_id: camera.stuemusikk
        name: stuemusikk_display