I have a number of aerial images that do not align with where my GPS says I am. For example, I am standing at the intersection of two roads with a Trimble R10 and a handheld IOS device with the aerial imagery as a geotiff displaying on it. The highly accurate GPS position is saying I am in the ditch about 6m away on the imagery. To rectify the imagery alignment issue I seem to be having I would imagine some program of placing Ground Control Points is necessary. My question is, how do you do this for aerial imagery that is already existing, not being flown at time of GCP collection. I know I need to find easily identifiable features on the aerial image but (1) I am in the middle of no-where and easily identifiable features are at a premium and (2) I will have to manually choose where I think the feature is on the image which could be off by up to, even over a meter thus defeating my Trimble's high accuracy. I think I am approaching this the only way you can, but want to see if there are different thoughts on the topic.