原文地址：http://blog.csdn.net/rhljiayou/article/details/10178723

效果图：

以下代码实现：
第一个图片的代码

//加阴影--任海丽编辑  
    _imageView.layer.shadowColor = [UIColor blackColor].CGColor;//shadowColor阴影颜色  
    _imageView.layer.shadowOffset = CGSizeMake(4,4);//shadowOffset阴影偏移,x向右偏移4，y向下偏移4，默认(0, -3),这个跟shadowRadius配合使用  
    _imageView.layer.shadowOpacity = 0.8;//阴影透明度，默认0  
    _imageView.layer.shadowRadius = 4;//阴影半径，默认3  

第二个图片的代码

_imageView1.layer.shadowColor = [UIColor yellowColor].CGColor;//shadowColor阴影颜色  
_imageView1.layer.shadowOffset = CGSizeMake(0,0);//shadowOffset阴影偏移，默认(0, -3),这个跟shadowRadius配合使用  
_imageView1.layer.shadowOpacity = 1;//阴影透明度，默认0  
_imageView1.layer.shadowRadius = 3;//阴影半径，默认3  

//路径阴影  
UIBezierPath *path = [UIBezierPath bezierPath];  
  
float width = _imageView1.bounds.size.width;  
float height = _imageView1.bounds.size.height;  
float x = _imageView1.bounds.origin.x;  
float y = _imageView1.bounds.origin.y;  
float addWH = 10;  
  
CGPoint topLeft      = _imageView1.bounds.origin;  
CGPoint topMiddle = CGPointMake(x+(width/2),y-addWH);  
CGPoint topRight     = CGPointMake(x+width,y);  
  
CGPoint rightMiddle = CGPointMake(x+width+addWH,y+(height/2));  
  
CGPoint bottomRight  = CGPointMake(x+width,y+height);  
CGPoint bottomMiddle = CGPointMake(x+(width/2),y+height+addWH);  
CGPoint bottomLeft   = CGPointMake(x,y+height);  
  
  
CGPoint leftMiddle = CGPointMake(x-addWH,y+(height/2));  
  
[path moveToPoint:topLeft];  
//添加四个二元曲线  
[path addQuadCurveToPoint:topRight  
             controlPoint:topMiddle];  
[path addQuadCurveToPoint:bottomRight  
             controlPoint:rightMiddle];  
[path addQuadCurveToPoint:bottomLeft  
             controlPoint:bottomMiddle];  
[path addQuadCurveToPoint:topLeft  
             controlPoint:leftMiddle];  
//设置阴影路径  
 _imageView1.layer.shadowPath = path.CGPath;  

ok！