Adding labels to merged foto's

I was wondering if it is possible to add a tag to a single photo in a merged item.
For example: I have personal files containing different documents of multiple photo’s Firstly I want to merge the photo’s beloning to one person/file into one item.
Then I want to label the item (the file) , as well as the individual photo’s/documents differently.
merged Item = file of Person x
photo 1= birth certificate
Photo 2= passport
photo 3 = baptism record
photo 4-6 = letter/correspondence

I want to create labels per photo. For example label to indicate I transcribed photo 3 and a label saying I am in the process of transcribing photo 1.
Now it just assigns the label to all the photos in the item. Is there another way to do this?

Currently labels can only be attached to the item; we’re probably going to allow tags at all levels in a future release.

(What you can already do is attach metadata fields at the photo level. So for example you could add a dc:type field to each photo.)