Geothings Map Warper
Geothings Map Warper (mapwarper.net) (previous version was hosted at warper.geothings.net) is an open-source map-warping / geo-rectifying service, written in Ruby on Rails and lets users import maps or aerial photos and warp/rectify them to fit into openstreetmap. Geothings is MIT licenced. The project was created by Tim Waters.
Note that there is a newer version of this project at Mapwarper.net with no limits on image size or dimensions.