Does the image get uploaded to a server?
No. Recognition runs with Tesseract compiled to WebAssembly in your browser, so the image and the extracted text stay on your device. Unusual for OCR, which is normally a cloud service.
Which languages are supported?
Twelve: English, Turkish, German, French, Spanish, Portuguese, Italian, Polish, Russian, Arabic, Japanese and Korean. Pick the language before you run it so the engine loads the right model; for a page that mixes in English, tick “Also read English words”. Each language downloads once, only when you pick it.
Why is some text wrong?
OCR is not perfect on low-quality or stylized input. A sharper, well-lit, straight-on image of printed text gives the best results.