Basic image editing

I need to do very basic editing of a large number of scanned images. They should be cleaned from stains and spots, the scanning "frame" should be removed, those that are skewed should be straightened up. ? In some images, contrast should be balanced to ensure readability. Again, this is VERY BASIC work. ? Nothing fancy. Worker would be paid in steps, according to progress. Images are JPG and the vast majority are 8.5 x 11 Could be as many as 25.000 images.