From the first message in this thread:

  automatic OCR / processing of all image files on macOS

If OCR was deferred until user request/consent, it would eliminate the battery/performance cost of speculative image analysis.

The first message in the thread isn't the definition of the actual feature.

What's the best way to disable all MacOS image processing background services?

There isn't any such service; it's on demand.

These macOS services appear to be related to image processing:

  photoanalysisd 
  mediaanalysisd
  com.apple.photos.backgroundAnalysisService