[MS] Add OCR layer service for embedded images and PDF scans (#1541)

* Add OCR test data and implement tests for various document formats

- Created HTML file with multiple images for testing OCR extraction.
- Added several PDF files with different layouts and image placements to validate OCR functionality.
- Introduced PPTX files with complex layouts and images at various positions for comprehensive testing.
- Included XLSX files with multiple images and complex layouts to ensure accurate OCR extraction.
- Implemented a new test suite in `test_ocr.py` to validate OCR functionality across all document types, ensuring context preservation and accuracy.

* Enhance OCR functionality and validation in document converters

- Refactor image extraction and processing in PDF, PPTX, and XLSX converters for improved readability and consistency.
- Implement detailed validation for OCR text positioning relative to surrounding text in test cases.
- Introduce comprehensive tests for expected OCR results across various document types, ensuring no base64 images are present.
- Improve error handling and logging for better debugging during OCR extraction.

* Add support for scanned PDFs with full-page OCR fallback and implement tests

* Bump version to 0.1.6b1 in __about__.py

* Refactor OCR services to support LLM Vision, update README and tests accordingly

* Add OCR-enabled converters and ensure consistent OCR format across document types

* Refactor converters to improve import organization and enhance OCR functionality across DOCX, PDF, PPTX, and XLSX converters

* Refactor exception imports for consistency across converters and tests

* Fix OCR tests to match MockOCRService output and fix cross-platform file URI handling

* Bump version to 0.1.6b1 in __about__.py

* Skip DOCX/XLSX/PPTX OCR tests when optional dependencies are missing

* Add comprehensive OCR test suite for various document formats

- Introduced multiple test documents for PDF, DOCX, XLSX, and PPTX formats, covering scenarios with images at the start, middle, and end.
- Implemented tests for complex layouts, multi-page documents, and documents with multiple images.
- Created a new test script `test_ocr.py` to validate OCR functionality, ensuring context preservation and accurate text extraction.
- Added expected OCR results for validation against ground truth.
- Included tests for scanned documents to verify OCR fallback mechanisms.

* Remove obsolete HTML test files and refactor test cases for file URIs and OCR format consistency

- Deleted `html_image_start.html` and `html_multiple_images.html` as they are no longer needed.
- Updated `test_file_uris` in `test_module_misc.py` to simplify assertions by removing unnecessary `url2pathname` usage.
- Removed `test_ocr_format_consistency.py` as it is no longer relevant to the current testing framework.

* Refactor OCR processing in PdfConverterWithOCR and enhance unit tests for multipage PDFs

* Revert

* Revert

* Update REDMEs

* Refactor import statements for consistency and improve formatting in converter and test files

packages/markitdown-ocr/src/markitdown_ocr/_plugin.py

@@ -0,0 +1,68 @@
+"""
+Plugin registration for markitdown-ocr.
+Registers OCR-enhanced converters with priority-based replacement strategy.
+"""
+
+from typing import Any
+from markitdown import MarkItDown
+
+from ._ocr_service import LLMVisionOCRService
+from ._pdf_converter_with_ocr import PdfConverterWithOCR
+from ._docx_converter_with_ocr import DocxConverterWithOCR
+from ._pptx_converter_with_ocr import PptxConverterWithOCR
+from ._xlsx_converter_with_ocr import XlsxConverterWithOCR
+
+
+__plugin_interface_version__ = 1
+
+
+def register_converters(markitdown: MarkItDown, **kwargs: Any) -> None:
+    """
+    Register OCR-enhanced converters with MarkItDown.
+
+    This plugin provides OCR support for PDF, DOCX, PPTX, and XLSX files.
+    The converters are registered with priority -1.0 to run BEFORE built-in
+    converters (which have priority 0.0), effectively replacing them when
+    the plugin is enabled.
+
+    Args:
+        markitdown: MarkItDown instance to register converters with
+        **kwargs: Additional keyword arguments that may include:
+            - llm_client: OpenAI-compatible client for LLM-based OCR (required for OCR to work)
+            - llm_model: Model name (e.g., 'gpt-4o')
+            - llm_prompt: Custom prompt for text extraction
+    """
+    # Create OCR service — reads the same llm_client/llm_model kwargs
+    # that MarkItDown itself already accepts for image descriptions
+    llm_client = kwargs.get("llm_client")
+    llm_model = kwargs.get("llm_model")
+    llm_prompt = kwargs.get("llm_prompt")
+
+    ocr_service: LLMVisionOCRService | None = None
+    if llm_client and llm_model:
+        ocr_service = LLMVisionOCRService(
+            client=llm_client,
+            model=llm_model,
+            default_prompt=llm_prompt,
+        )
+
+    # Register converters with priority -1.0 (before built-ins at 0.0)
+    # This effectively "replaces" the built-in converters when plugin is installed
+    # Pass the OCR service to each converter's constructor
+    PRIORITY_OCR_ENHANCED = -1.0
+
+    markitdown.register_converter(
+        PdfConverterWithOCR(ocr_service=ocr_service), priority=PRIORITY_OCR_ENHANCED
+    )
+
+    markitdown.register_converter(
+        DocxConverterWithOCR(ocr_service=ocr_service), priority=PRIORITY_OCR_ENHANCED
+    )
+
+    markitdown.register_converter(
+        PptxConverterWithOCR(ocr_service=ocr_service), priority=PRIORITY_OCR_ENHANCED
+    )
+
+    markitdown.register_converter(
+        XlsxConverterWithOCR(ocr_service=ocr_service), priority=PRIORITY_OCR_ENHANCED
+    )