I've used Windows Movie Maker, and i know for a fact that you can adjust the length of pictures, either manually or automatically
Manually, you just have to change the timeline display so that it actually shows the timeline instead of the preview images of the clips and hover over the edge of a picture/clip and click and drag until the length is as you want it to be
Auomatically, there's a setting in the options where you can change how long pictures last when they're put in the timeline