How do I stop the sprite window outline from showing?

If you look at the balloon you can see the square outline on the top left, it flickers when i run the game. However the balloon is a PNG image and there is absolutely no outline in the image. This outline also only shows IN Game. I even tried erasing in the corner just in case but it wasn't that. Anyone know why this is happening and how to stop it?

Actually it seems to be happening on multiple sprites. In the image you can also see it occurring just above the tents on the right as well