Purview on-demand classification to scan historical image files?

You identified the gap: Purview OCR processes only images uploaded after OCR is enabled, while on-demand classification targets historical files. Microsoft does not state that an on-demand scan retroactively triggers OCR for old images. Therefore, do not assume enabling OCR and launching a scan will extract text from the existing estate. Enable OCR for SharePoint and OneDrive so new supported images are scanned, then run a small on-demand classification estimate against a test site containing known historical images and review whether those extensions are eligible. Purview supports many image formats and scanned PDFs, subject to size and resolution limits, but support does not override the upload-after-enable restriction. For existing images that remain unprocessed, Microsoft documents no bulk re-OCR switch. Open a Microsoft support case for tenant-specific confirmation before touching production content. If re-uploading is considered, test copies first because it changes versions, timestamps, audit history, and potentially retention behavior.