Connected Still in Timeline

I have a connected still image above the main timeline. When I crop this still, or do a "Ken Burns" effect the main timeline shows around the edges where the still is cropped. Can this be hidden, if so does this apply to a connected clip also?

You are shrinking the size of the clip when you crop it, so yes, what's behind it (underneath) it will show. Increase the size of the connected still you cropped. The built-in Ken Burns effect will resize, when it can, to avoid this. If you won't want to resize the connected media, place a black "Solids" Generator under it (between it and the primary storyline below).