feat: Add LLM-based OCR as alternative to Tesseract (#2442)

* feat(ocr): add LLM-based OCR support alongside Tesseract

Add support for using configured LLM inference providers (OpenAI or Ollama)
for OCR text extraction from images as an alternative to Tesseract.

Changes:
- Add OCR_USE_LLM environment variable flag (default: false)
- Add buildOCRPrompt function for LLM-based text extraction
- Add readImageTextWithLLM function in asset preprocessing worker
- Update extractAndSaveImageText to route between Tesseract and LLM OCR
- Update documentation with the new configuration option

When OCR_USE_LLM is enabled, the system uses the configured inference model
to extract text from images. If no inference provider is configured, it
falls back to Tesseract.

https://claude.ai/code/session_01Y7h7kDAmqXKXEWDmWbVkDs

* format

---------

Co-authored-by: Claude <noreply@anthropic.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/docs/docs/03-configuration/01-environment-variables.md b/docs/docs/03-configuration/01-environment-variables.md
index 7a896fe4..dedc3406 100644
--- a/docs/docs/03-configuration/01-environment-variables.md
+++ b/docs/docs/03-configuration/01-environment-variables.md
@@ -176,13 +176,14 @@ Example JSON file:
 
 ## OCR Configs
 
-Karakeep uses [tesseract.js](https://github.com/naptha/tesseract.js) to extract text from images.
+Karakeep uses [tesseract.js](https://github.com/naptha/tesseract.js) to extract text from images by default. Alternatively, you can use an LLM-based OCR by enabling the `OCR_USE_LLM` flag. LLM-based OCR uses the configured inference model (OpenAI or Ollama) to extract text from images, which can provide better results for complex images but requires a configured inference provider.
 
 | Name                     | Required | Default   | Description                                                                                                                                                                                                                               |
 | ------------------------ | -------- | --------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
 | OCR_CACHE_DIR            | No       | $TEMP_DIR | The dir where tesseract will download its models. By default, those models are not persisted and stored in the OS' temp dir.                                                                                                              |
 | OCR_LANGS                | No       | eng       | Comma separated list of the language codes that you want tesseract to support. You can find the language codes [here](https://tesseract-ocr.github.io/tessdoc/Data-Files-in-different-versions.html). Set to empty string to disable OCR. |
 | OCR_CONFIDENCE_THRESHOLD | No       | 50        | A number between 0 and 100 indicating the minimum acceptable confidence from tessaract. If tessaract's confidence is lower than this value, extracted text won't be stored.                                                               |
+| OCR_USE_LLM              | No       | false     | If set to true, uses the configured inference model (OpenAI or Ollama) for OCR instead of Tesseract. This can provide better results for complex images but requires a configured inference provider (`OPENAI_API_KEY` or `OLLAMA_BASE_URL`). Falls back to Tesseract if no inference provider is configured. |
 
 ## Webhook Configs