If you have System 7 Pro (and an RSA certificate), you can sign any file, including a picture stored as EPSF or TIFF or whatever by dropping the file on your signature -- there are no modifications needed to the application that created the file. An application can sign pieces of information within a file (such as the content of a dialog, or the position of an object) by adding a small amount of code that calls the Digital Signature Manager. File signatures are verified by the Finder (or by an application), while object signatures are verified by the application. The developer toolkit has sample code that shows how to manage digital signatures, including a drawing program with signed objects and a Think C class library for signed files and objects. Martin Minow minow@apple.com The above does not represent the position of Apple Computer Inc.