I have never tried to write on photos, but had a similar situation at work. One of our colleagues decided to move abroad and we decided to gift him a framed photo of our team. We wanted to sign the photo but didn't want the signatures to fade. After some trial and error, we used white waterproof marker for writing on various surfaces to sign the photo and framed it afterwards. It looked really awesome.
I know it is not exactly what you aimed for, but give it a shot, I was pleasantly surprised with the result. Just remember to print out 5-10 pieces, so you can try lots of stuff out.