Because AE notes the xy location of the Anchor Point when keeping track of a layer's position, a shift in the anchor point within the layer will cause the images on that layer to move. Changing the anchor point using the Move Tool (V) moves the anchor point relative to the layer itself, resulting in movement of the element in the Comp.

Let's work an exercise to develop an understanding and the ability to do this last move...

1) Download this file and use one of the backgrounds within the ZIP. Import them into a new Project as Footage and note their size 1920 x 1080.

2) Create a new Comp and set the size to the Preset NTSC DV: 720 x 480. Set the length at 10 seconds.

3) Drag the background image you chose down into gray area just to the left of the Timeline. This will place the image inside the Comp sitting directly in the center of the stage. This is important. For this technique to work, the Footage Anchor Point MUST be sitting at the center of the Comp.

4) Double-click on the Layer Name of this Footage and note that the Comp tab has been replaced by the Layer tab, showing the entire image. To better see the results in the Comp tab, Right-Click on the Layer tab name at the top of the Window and choose Undock Panel. Resize and relocate this free window so you can see both it and the contents of the Comp tab.

5) Locate the Anchor Point at the center of the Footage Window and use the Move Tool (V) to pull it around the scene. Note that the position of the camera in the Comp appears to move. And at all times the Anchor Point remains at the center of the Comp. This allows you to Scale the image up and down and always be able to push into and pull out of the area of interest. Scale the image and see how it no longer pulls off center as you do.

6) To animate these moves, highlight the Footage in the Timeline and hit S to bring up Scale track. Now hit Shift-A to also show the Anchor Point track..