When solving the "match this silhouette" before moving to the next level, you can either attempt to find the correct shape by observation or you can try all until you find the right one.
If opting for the latter, one must note that when you "restart" the shadow images change position and rotate around the screen from one side to another.
Therefore the best choice is to pick ONE shadow and constantly test it to see if it fits. Personally I choose the middle directly left of the central figure, but it makes no difference as long as you stick with your choice. Every time you restart and have to choose, select the same figure. Eventually you will have the correct one as it will have rotated through the options.