Forensic tools are used to create critical evidence in computer-related crimes investigation. The evidence has an effect on judgment by the court and it requires verification of forensic tools. The verification should require an agreement of law enforcement organizations. Computer Forensic Tool Testing (CFTT) Verification project provides a measure of assurance that the tools used in the investigations produce valid results . CFTT suggests requirements, assertions and test cases document for verification of forensic tools. There are hidden data in acquired image however CFTT do not deal with detection test on hidden data. Detection technology depends on cover carriers, such as images, audio, text or code represented digitally, hold the hidden data. This paper proposes preprocesses for detection of hidden data to be existed or not by forensic tools.