Fingerprinting is an important preliminary step when auditing Web applications. But the usual techniques based on the analysis of cookies, headers and static files are easy to fool. Fingerprinting digital images is a technique commonly used for forensic investigations but rarely for security audits. Moreover, it is mostly based on the analysis of JPEG images only. In this webcast, the presenter will study the implementation differences between number of PNG decoders/encoders, either build-in or commonly used with the main web application development platforms.