思路：首先我的思路放两个imageView在Controller里把高清的图片放在下面，带有毛玻璃效果的图片放在上面。

//在Controller的view上加一个手势代码如下（温馨提示，开启imaegView的触摸事件）

UIPanGestureRecognizer * pan = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(pan:)];

[self.view addGestureRecognizer:pan];

//然后就是把我们触摸到的周边擦去代码如下

CGPoint point = [pan locationInView:self.view];

CGFloat x = point.x - 10;

CGFloat y = point.y - 10;

CGFloat W = 20;

CGFloat H = 20;

CGRect rect =  CGRectMake(x, y, W, H);

UIGraphicsBeginImageContextWithOptions(self.view.bounds.size, NO, 0.0);

CGContextRef ctx = UIGraphicsGetCurrentContext();

[self.bgTopImageView.layer renderInContext:ctx];

CGContextClearRect(ctx, rect);

UIImage * newImage = UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();

self.bgTopImageView.image = newImage;

效果图