incremental segmentation

[bertsky]

ocrd_tesserocr/ocrd_tesserocr/recognize.py

Lines 370 to 375 in ac27465

	# FIXME: We should somehow _mask_ existing regions in order to annotate incrementally (not redundantly).
	# Currently segmentation_level=region also means removing regions,
	# but we could have an independent setting for that, and attempt
	# to detect regions only where nothing exists yet (by clipping to
	# background before, or by removing clashing predictions after
	# detection).