What do u mean by Image rectify and how we can perform this task by ERDAS imagine?

Image rectify mean georefrence the image to it’s real location and true scale on the earth so when measure the distance or calculate area the result will be real area or distance on ground also if locate point by lat/lon or X/Y collecte from GPS for example this point located correctly in the true location

To georeference the image by ERDAS Imagine2011 check this link: https://www.youtube.com/watch?v=kbeGJRZzmB8&index=39&list=PLZCBevgc6L5XGU3POIr0gCUg0w8puoLSe