Hi Sam - thanks for getting back to me so quickly!
It's not the EXIF data I'm talking about.
On a photo page there is a section called Additional Info. In the new layout it is between the Tags section and the Owner Settings section. I think that it may have been in that location on the old Flickr photo page layout as well. If you edit a photo via
Picnik and save as a new photo then the Additional Info field is where this information is displayed: "Uploaded using Picnik". As my application can upload and manage my photos I was wanting to use this field to display a similar string.