PICT file format information is available from APDA (Apple Programmers and Developers Assn.) (408/562-3910). In addition, Inside Macintosh Volume V describes the PICT file format. The earlier versions of Inside Mac also have limited descriptions of PICT file formats.
The PICT file format for MacDraw II is available from Claris Technical Support. This document includes the information about the PICT header for MacDraw II files. This information is not proprietary and does NOT require a Non-Disclosure Agreement.