1. A system comprising: a computer system running image processing software that when executed by the computer system causes the computer system to: receive an identification of a desired area to be imaged and collected into an oblique-mosaic image; create a mathematical model of a virtual camera having a sensor higher in elevation from which source oblique images were captured and looking down at an oblique angle, the mathematical model having an oblique-mosaic pixel map for the sensor of the desired area encompassing multiple source images; assign a surface location to each pixel included in the oblique-mosaic pixel map; select source oblique images of geographic coordinates captured at an oblique angle and compass direction similar to the oblique angle and compass direction of the virtual camera; and reproject at least one source oblique image pixel of the area to be imaged for each pixel included in the oblique-mosaic pixel map in a fan-like pattern to thereby create an oblique-mosaic image of the desired area.