If by tagging you mean Identifying the photo the best way is to use a photo editing program like irfanview. You can expand the picture for the information or add it to some part of the picture. Either way you can add all of the id information right to the picture.
When somebody who uses the picture, either attaching it to their tree or downloading it, your ID information will be a permanent part of the picture and always be there..
When somebody who uses the picture, either attaching it to their tree or downloading it, your ID information will be a permanent part of the picture and always be there..