The scanframes option can be used to get a fast initial alignment and also to find a good image to be used as a reference during alignment.

This image shows the 1st frame of the sequence we will process using Scanframes.

After pressing Set Alignpoints this set of Alignpoints is shown. You can also set the alignpoints yourself, scanframes will use the 5 "strongest" alignpoints.

You can see where the 5 strongest alignpoints are if you move the Alignpoints slider to the right until only 5 alignpoints are shown. These 5 alignpoints will be used during scanframes to do a fast intial alignment and also select frames on quality.

This image shows the result of using Scanfames. The large red box shows the part of this frame that is visible on all frames, the fact that this box is more or less filling the full image shows that the sequence doesnt have much movement between the frames. After using Scanframes RegiStax automatically calls "Set alignpoints". If you are happy with these alignpoints you can immediately proceed by pressing ALIGN.