Question: I'm building an iPhone app that, among other things, allows the user to take and store photographs associated with locations. I am currently using the ALAssetLibrary to allow the photographs to be stored in Photos and be accessible outside the app (on a computer for instance via the built-in mechanisms). There is not a lot of technical content out there for working with the ALAssetLibrary but from what there is I have managed to cobble together a working version of this. I have had to resort to storing a dictionary of photo URLS in my app and manually detecting if the photo still exists when displaying lists of them because there does not seem to be a way to add custom metadata to an ALAsset.

What I would really like to do is add two custom metadata fields to each asset to provide it with a title and a custom id value that I can use to filter on when enumerating the asset library.

As a secondary task, I'd like the user to be able to update the title metadata.

Can it be done? At this point, I really don't think it can because the API really doesn't seem to provide the necessary methods to get/set custom metadata. I'm hoping against all odds that there is some other aspect to the AssetLibrary framework that I have not yet discovered.

At a minimum, if someone can authoritatively say "NO" then at least others might find this breadcrumb on their own trail of hope and change tack more quickly!

And, having 0 reputation I can't tag it with AssetLibrary :( wow, this day is just going downhill. FML

Answer: 
I've been looking over the documentation and I dont think it is possible to tack on additional fields to the ALAsset object, well you can create your own object or extend theirs but that wont help you when your pulling back assets because you'll need to init yours and populate it then.

Look I know this falls short of a really good answer but I had to try.
The ALAsset class documentation describes a property - customMetadata. This is documented to be an NSDictionary of whatever custom tags you want. Currently, however, it is not implemented in the class (I've raised a bug on Apple's developer site to bring the issue up).