如何在各自的图像视图中制作正确的图像？

Here i want to drag and drop correct image i.e alphabet A from left side to its image on right side and set the score rise by 1. But after writing following code all the image get disappear when dropping outside of view. And also all the images make the score rise along with the correct one. Can anyone help me in this ??Here i want to drag and drop correct image i.e