We are adding the ability to draw on the photos (circle, highlight, arrows) in our next release of Pruvan Mobile. (Q1-2014)
You can use the Pencil icon to add notes to the photos and these will be available as a caption. We are thinking on adding the ability to allow Notes, Evidence Types, etc to be added to the File name when the photos are downloaded using the PRuvan Downloader. Please see related Idea.