Different formats and compression algorithms have been proposed for 3D video content, but 3D images are still mostly represented as a stereo pair only. However, for enhanced 3D rendering capabilities, such as depth perception adjustment or display size adaptation, additional depth data is necessary. To facilitate the standardization process of a common 3D format, backward compatibility with legacy technologies is necessary. In this paper, we propose to extend the JPEG file format, as the most popular image format, in a backward compatible manner to represent a stereo pair and additional depth data. We propose an architecture to achieve such backward compatibility with JPEG. The coding efficiency of a simple implementation of the proposed architecture is compared to the state of the art stereoscopic 3D image compression and storage formats.