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 geographical area to be imaged and collected into an oblique-mosaic image; create a mathematical model of a virtual camera looking down at an oblique angle, the mathematical model having an oblique-mosaic pixel map of the desired geographical 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; create a ground elevation model of the ground and vertical structures within the oblique-mosaic pixel map using overlapping source images; and reproject source oblique image pixels of the area to be imaged for pixels included in the oblique-mosaic pixel map using the ground elevation model to thereby create an oblique-mosaic image of the desired area.