加载所有照片

iOS 9 后用：PHPhotoLibrary

 ALAssetsLibrary *library = [[ALAssetsLibrary alloc]init];
    
    [library enumerateGroupsWithTypes:ALAssetsGroupSavedPhotos usingBlock:^(ALAssetsGroup *group, BOOL *stop) {
        
        [group enumerateAssetsUsingBlock:^(ALAsset *result, NSUInteger index, BOOL *stop) {
            
            NSLog(@"%@",result);
            CGImageRef image = result.thumbnail;
        }];
    } failureBlock:nil];