给UIImageview 添加边框 或者设置成圆角

 //设置layer
 CALayer *layer=[backView layer];
 //是否设置边框以及是否可见
 [layer setMasksToBounds:YES];
 //设置边框圆角的弧度
 [layer setCornerRadius:10.0];
 //设置边框线的宽
 //
 [layer setBorderWidth:1];
 //设置边框线的颜色
 [layer setBorderColor:[[UIColor blackColor] CGColor]];

扩展思维：不管什么控件 我们都是通过设置边框线都可以改变她的形状 

 //给iamgeview添加阴影  和边框
 UIImageView * imgvPhoto = [UIImageView alloc] init];
 //添加边框
 CALayer * layer = [_imgvPhoto layer];
 layer.borderColor = [
     [UIColor whiteColor] CGColor];
 layer.borderWidth = 5.0f;
 //添加四个边阴影
 _imgvPhoto.layer.shadowColor = [UIColor blackColor].CGColor;
 _imgvPhoto.layer.shadowOffset = CGSizeMake(0, 0);
 _imgvPhoto.layer.shadowOpacity = 0.5;
 _imgvPhoto.layer.shadowRadius = 10.0;给iamgeview添加阴影 < wbr > 和边框
 //添加两个边阴影
 _imgvPhoto.layer.shadowColor = [UIColor blackColor].CGColor;
 _imgvPhoto.layer.shadowOffset = CGSizeMake(4, 4);
 _imgvPhoto.layer.shadowOpacity = 0.5;
 _imgvPhoto.layer.shadowRadius = 2.0;