This paper describes a multi-image fusion techniques that makes possible the building of extremely large phototriangulation networks (900 km × 900 km) based on TK-350 Russian satellite imagery. Substitution of highresolution imagery around ground control points and tie-points of low-resolution imagery in the development of photogrammetric networks may significantly increase the accuracy of such networks. Furthermore, substitution of high-resolution images for both components of a low-resolution stereopair while maintaining the high-resolution image geometries may provide a capability to obtain new DEM products with higher levels of detail. The challenge of the research described in this paper was to develop a photogrammetric approach for such fusion, combining images having significant differences in resolution and sensor models. The goals of the algorithms and software developed are the creation of a stereopair, conforming low-resolution imagery optimal geometry with high-resolution details. Theoretically the method is generic and applicable to any image sources. This article presents the innovative research approach in more detail. TK-350 imagery has a normalized cost of only 11¢ per km 2, and thus represents a potential source of relatively inexpensive imagery covering large areas. In particular, the approach presented may be feasible for generating DTED® Level 2, and so may prove useful in extending such data to higher latitudes and other areas not covered by the Shuttle Radar Topography Mission.