1. An image processing system with an image conversion unit that composites overhead view images obtained by converting viewpoints of photographed images of a plurality of cameras, comprising: an image detection unit that extracts image feature amounts from the respective photographed images of the plurality of cameras, wherein the image conversion unit, in regard to a superposition area that is photographed by the plurality of cameras overlappingly, sets blend rates for the entire of the superposition area or in units of pixels in accordance with the image feature amounts extracted by the image detection unit, composites the overhead view images corresponding to the superposition area at the blend rates and performs composition by changing a blend rate setting method in accordance with a correlation between the image feature amounts of the respective overhead view images in the superposition area.