All the Analyzing GME effects have two on-screen widgets: one to provide feedback and one to set up the analysis region.
Analysis Region Widget - This is a rectangle widget which you use to set the analysis region over the reference image.
Four Corner Widget - This is a widget that shows the state of the four-corner pin that has been calculated. You can change it by grabbing any of the corners and tweaking the shape of the pin. To give you more feedback as to what frames have been analyzed, it will be drawn solid if there is a key in the corner pin at the frame being displayed; otherwise, it will be drawn dashed.