Based on my recent experience with this pytesseract error on Windows, I have written different steps in sequence to make it easier to resolve the error:
1. Install tesseract using windows installer available at: https://github.com/UB-Mannheim/tesseract/wiki
2. Note the tesseract path from the installation. Default installation path at the time of this edit was: C:\Users\USER\AppData\Local\Tesseract-OCR. It may change so please check the installation path.
3. pip install pytesseract
4. Set the tesseract path in the script before calling image_to_string:
pytesseract.pytesseract.tesseract_cmd = r'C:\Users\USER\AppData\Local\Tesseract-OCR\tesseract.exe'