A page may carry an optional /Thumb image XObject (ISO 32000-2 12.3.4),
a miniature rendering used only as a navigation aid. OCRmyPDF alters
page appearance (deskew, clean, rasterize, re-render) and plugins may
edit pages arbitrarily, so a retained thumbnail would be stale and no
longer match its page. Modern viewers generate thumbnails on demand, so
there is no loss of functionality.
OcrGrafter.finalize() now strips /Thumb from every page before saving,
alongside the existing search-index discard, covering both the OCR and
hOCR pipelines. Orphaned thumbnail XObjects are garbage-collected on save.