This document discusses techniques for detecting counterfeit Indian currency notes. It begins with an overview of common counterfeit detection methods used by the Reserve Bank of India, such as seeing through the register, checking the watermark, examining fluorescence under UV light, and verifying the security thread. The document then reviews related work on counterfeit currency detection using techniques like feature extraction and image processing. It focuses on preprocessing techniques for counterfeit detection, including image adjustment, filtering, smoothing, and color space conversion.