试试这段代码：

在此路径中保存图片：

 NSFileManager *fileMan = [NSFileManager defaultManager];

    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];

    NSString *str= [NSString stringWithFormat:@"%@.png",patientlastName];
   NSString *Image_filePath=[documentsDirectory stringByAppendingPathComponent:str];
 NSData *imagedata=UIImagePNGRepresentation(yourimage);
 [fileMan createFileAtPath:[Image_filePath stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding] contents:imagedata attributes:nil];

获取图片路径：

NSString* fileName = [NSString stringWithFormat:@"%@.png",patientlastName}
        NSArray *arrayPaths =
        NSSearchPathForDirectoriesInDomains(
                                            NSDocumentDirectory,
                                            NSUserDomainMask,
                                            YES);
        NSString *path = [arrayPaths objectAtIndex:0];
        NSString* pdfFileName = [path stringByAppendingPathComponent:fileName];

      UIImage *image1=[UIImage imageWithContentsOfFile:pdfFileName];
       imageView.image=image1;