ALAssetsLibrary delete ALAssetsGroup / ALAsset

You can only delete the ALAsset which is created by your app with document API [ALAsset setImageData:metadata:completionBlock:] (But I have not found any API to delete a ALAssetGroup).

1). Add an image "photo.jpg" to your project 2). Save an image to asset library:

ALAssetsLibrary *lib = [ALAssetsLibrary new];
UIImage *image = [UIImage imageNamed:@"photo.jpg"];
[lib writeImageToSavedPhotosAlbum:image.CGImage metadata:@{} completionBlock:^(NSURL *assetURL, NSError *error) {
    NSLog(@"Write image %@ to asset library. (Error %@)", assetURL, error);
}];

3). Go to default gallery, you will find photo.jpg in your "Saved Photos" album.

4). Delete this image from asset library:

ALAssetsLibrary *lib = [ALAssetsLibrary new];
[lib enumerateGroupsWithTypes:ALAssetsGroupSavedPhotos usingBlock:^(ALAssetsGroup *group, BOOL *stop) {
    [group enumerateAssetsUsingBlock:^(ALAsset *asset, NSUInteger index, BOOL *stop) {
        if(asset.isEditable) {
            [asset setImageData:nil metadata:nil completionBlock:^(NSURL *assetURL, NSError *error) {
                NSLog(@"Asset url %@ should be deleted. (Error %@)", assetURL, error);
            }];
        }
    }];
} failureBlock:^(NSError *error) {

}];

5). Go to default gallery, you will find photo.jpg has already been deleted.

This is not possible using any documented API. Only the photos app can delete Albums. If you want this feature to be added to iOS, I would fill a feature request at https://feedbackassistant.apple.com/.

in ios8 deleting photos might be possible using the Photos Framework

Please check the documentation of Photos Framework

For deleting assets refer to PHAssetChangeRequest

+ (void)deleteAssets:(id<NSFastEnumeration>)assets

where assets is an array of PHAsset objects to be deleted.

For deleting collections refer to PHAssetCollectionChangeRequest

+ (void)deleteAssetCollections:(id<NSFastEnumeration>)assetCollections

https://developer.apple.com/library/prerelease/ios/documentation/Photos/Reference/PHAssetChangeRequest_Class/index.html#//apple_ref/occ/clm/PHAssetChangeRequest/deleteAssets: