Saving pictures to custom photos album then reloading

I'm trying to save an image to the photos album. But then I want to save some kind of reference to where it is, so that I can save it (using NSKeyedArchiver), close the app... and then be able to open the app again and reload the image. I'm not seeing how to do this. This is how I'm saving the image... how do I save a reference to it. I tried to save the assetURL variable within the completion block, but I was unable to do so... Would appreciate any help.

[selfwriteImageToSavedPhotosAlbum:image.CGImageorientation😟ALAssetOrientation)image.imageOrientation

completionBlock:^(NSURL* assetURL, NSError* error) {

//error handling

if (error!=nil) {

completionBlock(error);

return;

}

}];