In this paper we focus on the long-term stability of existing image file formats and possible new standards for archival purposes. It will be shown what significance digital file formats in a digital preservation workflow have and how they affect the success of digital archiving. Besides basic format requirements, like following an open standard and being widely used, we will discuss technical details of existing format definitions and their ability to encapsulate metadata for successful preservation. Based on the well-known Tagged Image File Format (TIFF) we will show in detail what weaknesses exist, that endanger the correct future rendering of the content. As a result a recommendation for an image file format definition for archival needs is proposed, based on the already existing widespread and accepted standard TIFF. The proposed approach follows the concept of a limited subset of a given file format like it is done with the Portable Document Format (PDF) and its archival derivative PDF/A. The approach results in a recommended use of the TIFF baseline specification. We call the optimized application of the existing file format TI/A, Tagged Image for Archives.